GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: Scotchmo on March 12, 2020, 05:28:02 PM
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I was going to get a JSAR Raptor for some 100yd benchrest matches. But I decided to go another route.
I'm starting with a new .22 caliber Benjamin Armada. I considered getting a .25 caliber, but .22 caliber affords more shooting opportunities at the various long range bench rest matches. The Armada will be configured as follows:
Main tube will act as a 215cc plenum
450cc, 4500psi bottle, slung under the main tube, regulated up to 3000psi
700mm barrel liner, under tension in a CF tube
electronic hammer
micro-switch trigger
4 different dwell setting in the electronics, instantly accessible
I'm going for the following performance:
Dwell 1: 20-25fpe with 9-15gr projectiles, 120 shots/fill
Dwell 2: 40-50fpe with 18-25gr projectiles, 60 shots/fill
Dwell 3: 60-75fpe with 25-34gr projectiles, 40 shots/fill
Dwell 4: 80-100fpe with 34+gr projectiles, 30 shots/fill
The object is to be able to shoot a large range of projectile weights, in the 880-1080fps range. Lower dwell settings for light pellets so that they don't go supersonic, and longer dwell for heavier pellets/slugs to get them into the high subsonic range.
As part of the process, I've been updating my PCP simulation spreadsheet. The spreadsheet was initially done to track Lloyds supersonic dump gun tests. I've added some more features to it to model a gun with a knock open valve with controllable dwell.
I've been working on the design and ordering parts/components. Initially, I ordered some of the parts from China, so am getting too long delays. I'm trying to order from the USA for the rest of the build. I'll post more in this thread as the design/build progresses.
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I made a bottle holder/bracket for the Armada. The Armada has an M-lok mounting system on the handguard - very convenient for mounting things. I designed the mounts in AutoCAD, sliced it in Cura, and 3D printed it on my Anycubic Delta Plus.
(http://www.scotthull.us/photos/Armada/Armada-brkt-bottle.jpg)
(http://www.scotthull.us/photos/Armada/Armada-sleeve-bottle.jpg)
I was getting some clogging in the nozzle so the finish did not turn out so good on this part. It works fine but I might print another one later on. I cleaned the nozzle out after this and subsequent prints got much better.
(http://www.scotthull.us/photos/Armada/IMG_2344.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2346.JPG)
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nice work Scott.. Very curious to see the electronics layout..
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nice work Scott.. Very curious to see the electronics layout..
I'm still waiting on some of the individual components, but here is the circuit diagram and control box design:
(http://www.scotthull.us/photos/Armada/Armada-circuit.jpg)
The circuitry will be housed in a control box which will mount on the left side of the rifle handguard, above the bottle, via M-lok.
(http://www.scotthull.us/photos/Armada/Armada-box-control.jpg)
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this is wild (-;
im guessing the battery is an RC battery and will be charged with an external BMS/ charger. Is the hammer directly connected to the shaft/armature of the solenoid to retard bounce , or some other mechanism ?
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Are there supposed to be pictures? ???
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this is wild (-;
im guessing the battery is an RC battery and will be charged with an external BMS/ charger. Is the hammer directly connected to the shaft/armature of the solenoid to retard bounce , or some other mechanism ?
The battery is likely a drone/helicopter battery. Similar to this one:
https://www.ebay.com/itm/223486362101 (https://www.ebay.com/itm/223486362101)
I would prefer a single cell (1S) for simplicity, but decided to go with 2S to better drive the boost converter. Only two cells, and no intermediate connection, so I'll forego the BMS and use a low charge rate. It should be OK:
https://www.ebay.com/itm/172438873872 (https://www.ebay.com/itm/172438873872)
The solenoid "armature" (plunger) IS the hammer. The holding force is highest with the valve fully open. I don't think bounce will be a problem.
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Are there supposed to be pictures? ???
There are pictures. They are not showing for you?
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Very cool, Scott.... Does the bottle feed into the gauge port?....
Bob
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Very cool, Scott.... Does the bottle feed into the gauge port?....
Bob
Yes. I replaced the gauge with a male Foster fitting.
The fill port will be on the bottle, and the original fill port up front will likely be replaced with a bleed screw/valve to degas the plenum.
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Are there supposed to be pictures? ???
There are pictures. They are not showing for you?
Nope. Not even showing a broken link icon... It's just blank spaces.
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Are there supposed to be pictures? ???
There are pictures. They are not showing for you?
Nope. Not even showing a broken link icon... It's just blank spaces.
They are externally linked pictures displayed as embedded images. No logging in needed. I don't know why they are not showing for you.
Here are the URLs for the pictures so you can view them externally.
http://www.scotthull.us/photos/Armada/Armada-brkt-bottle.jpg (http://www.scotthull.us/photos/Armada/Armada-brkt-bottle.jpg)
http://www.scotthull.us/photos/Armada/Armada-sleeve-bottle.jpg (http://www.scotthull.us/photos/Armada/Armada-sleeve-bottle.jpg)
http://www.scotthull.us/photos/Armada/IMG_2344.JPG (http://www.scotthull.us/photos/Armada/IMG_2344.JPG)
http://www.scotthull.us/photos/Armada/IMG_2346.JPG (http://www.scotthull.us/photos/Armada/IMG_2346.JPG)
http://www.scotthull.us/photos/Armada/Armada-circuit.jpg (http://www.scotthull.us/photos/Armada/Armada-circuit.jpg)
http://www.scotthull.us/photos/Armada/Armada-box-control.jpg (http://www.scotthull.us/photos/Armada/Armada-box-control.jpg)
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I really appreciate those links! I'm not sure why the pics in the other posts don't work either- usually I have no issues like this from this forum on this computer...
I like it!!
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Note: I did make a change to one wire in the circuit layout so that the additional caps don't keep charging when the trigger is being pulled.
I'm still waiting on some parts, but I had enough not-quite-right parts laying around to do a trial assembly and test. The higher voltage boost converter came in, but I'm still waiting on the 2S lithium charger and 35v caps. For now I assembled with the 1S battery and 25v caps. It works but the low voltage results in a very low charge current. So I would need to wait a long time between shots. I would like the cap charge time to be <3 seconds in it's final form.
Since we are all being encouraged to stay home because of the coronavirus, I spent all of yesterday and part of today soldering wires. Very tedious work and my eyes are not that great for close up work. I need lots of light. I'll probably get a lighted magnifier if I continue to work on projects like this one.
First picture shows the control box "OFF" (0). The red switch turn the system on and charges the right most cap. Each additional black switch can engage an additional cap:
(http://www.scotthull.us/photos/Armada/Armada-box-00.jpg)
Powered on and one addtional cap engaged. The lower right meter is the batter voltage. The bank of four meters indicate the capacitor voltages. The plan is to use 35v for caps when they arrive.:
(http://www.scotthull.us/photos/Armada/Armada-box-01.jpg)
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everything looking great .. how much bigger are the 35v caps ?? also, can this gun take us back to 1985 ?
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everything looking great .. how much bigger are the 35v caps ?? also, can this gun take us back to 1985 ?
They will all be 18mm dia caps. The maximum length (40mm) are those shown. These industrial grade caps are 12,000uf@25v and 7500uf@35v. The caps that I'm waiting on are commercial grade (cheaper) but are the same physical size. They will be 6800uf@35v. I can get shorter caps if want to . I might do that later. Caps of all the same capacity gives me four different dwell settings. If I use multiple sizes for the additional caps, I could use different switch combinations to get eight different dwell levels.
https://no.mouser.com/datasheet/2/293/UBY_e-1280407.pdf
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More details. I needed to tear it down again to work on the wiring harness.
Bottle can be removed...
(http://www.scotthull.us/photos/Armada/IMG_2354.JPG)
after degassing the plenum:
(http://www.scotthull.us/photos/Armada/IMG_2355.JPG)
I need to run four wires to the solenoid and trigger. I'm thinking of using bullet connectors on each end to connect a four wire harness that runs front-to-back. I'll need to mill out a few small areas in the plastic receiver in order to pass the wires through. That means a trip to the shop (and milling machine) - maybe tomorrow...:
(http://www.scotthull.us/photos/Armada/IMG_2356.JPG)
I printed a housing for the trigger group which consists of the Marauder trigger blade and a microswitch. The housing is adjustable front to back. And there are two setscrew adjustments for freeplay and travel limit.
(http://www.scotthull.us/photos/Armada/IMG_2358.JPG)
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this is brilliant. And very good employment of the 3d printer.
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subscribing. this is awesome..
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Spent some solitary time in the shop working on some of the metal/machined parts. I'm an amateur machinist and I work very slowly when making metal parts. It would sure be nice if I could 3D print everything. I've done trial fitting of most of the parts. I still have more to do, and then some sub-assembly testing, and then final assembly and shooting at the range - I'm getting excited about that but need to be patient. I have some more machining to do and I also have a few more necessary items coming in the mail. Here is what I've done so far:
(http://www.scotthull.us/photos/Armada/future-airgun.jpg)
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lookin good !
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I got a couple of critical parts made today in the shop. One of them was the thimble which still needs some hand blending of the transfer port (Motorhead said it helps flow, so I'm going to do it). I use thimbles as I find porting a barrel directly to be too stressful. Too easy to mess up an expensive barrel. If I mess up a thimble, or want to change it, only 50 cents worth of brass is wasted. I'm still waiting on some Loctite 641 (temporary bonding of cylindrical parts), and some Loctite 648 (high strength bonding of cylindrical parts). They should be here early next week and then I can do the assembly to test. I was going to do a shrink fit on some of the parts but decided against it. Very hard to undo a shrink fit if it messes up. I'm giving these specialty Loctite solutions a try for the first time. The shear strength rating is plenty for the expected loads.
(http://www.scotthull.us/photos/Armada/IMG_2365.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2366.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2367.JPG)
This is turning into a complicated project. Assembly order is important. And overall assembly is time consuming. It would be near impossible to fix some of the things in the field. But it's a benchrest specific gun, so that's OK.
Originally was going to be regulated to 3000psi, but I'm might get the performance desired at 2000psi, and that will almost double the shot count.
Two things I'm still planning for it - a fixed AR target stock. A moderator (DonnyFL Sumo maybe?)
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That is some Buck Rogers looking stuff. Great job.
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Wild looking gun, Scott.... I love the clear cover over the electronics.... I hope it works as good as it looks.... 8)
Bob
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I am considering something like this. Thank you for sharing your work here.
I do have a couple of questions.
What solenoid are you using that is strong enough to knock open the valve. With such a low duty cycle, I would suspect it could be overdriven from rated voltage.
What does the time open (dwell) need to be? I’m aware this is relative to several things, just wondering a range. Microseconds? Milliseconds?
I was thinking of using an Arduino to fire a mosfet for an adjustable (by pot) amount of time. I wrote a sketch for it but was wondering what time window I needed to map the pot output for.
Thanks again,
Dave
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A range of from 0.5-3.0 mSec. should cover most situations....
Bob
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I am considering something like this. Thank you for sharing your work here.
I do have a couple of questions.
What solenoid are you using that is strong enough to knock open the valve. With such a low duty cycle, I would suspect it could be overdriven from rated voltage.
What does the time open (dwell) need to be? I’m aware this is relative to several things, just wondering a range. Microseconds? Milliseconds?
I was thinking of using an Arduino to fire a mosfet for an adjustable (by pot) amount of time. I wrote a sketch for it but was wondering what time window I needed to map the pot output for.
Thanks again,
Dave
http://www.solenoidcity.com/solenoid/tubular/s-20-90hp1.htm (http://www.solenoidcity.com/solenoid/tubular/s-20-90hp1.htm)
The 22 and 23 AWG versions are good candidates for 25-35 volt systems. You could use the other gauges but would probably need to up the voltage to drive them. The cycle is low milliseconds so they can be over-driven without over-heating. The maximum shown for the 22 AWG version is 7.1v, but I have been driving it at 25v and plan on going to 35v.
Bob is right on for time. My spreadsheet shows that with 2000psi, I can drive a 14.3gr pellet at about 800fps with a .0005s dwell, and I can drive a 40gr projectile to about 1000fps in a 28" barrel, using .003s dwell. So 0.5-3.0 milliseconds should cover the range of what I want to do. My system has no digital controls. I fire the capacitors off through an SCR. Once the voltage in the capacitors decays sufficiently, the valve closes. I use the time constants of the capacitors to control the dwell time. Part of the run-time is used to accelerate the plunger, and knock the valve open. And there is some dwell from the inertia (mass) of the plunger once the valve is opened. Additional time (added capacitance) is used to hold the valve open longer. Once the holding force of the solenoid falls below the closing force on the valve, the valve closes. I have four switches that control which/how-many capacitors get charged. Can you control the mosfet with a small enough time resolution? The computer controlled mosfet would likely give you better control, but currently beyond my electronics ability.
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I finished up the thimble today. My eyes aren't that good for small/close-up work, so though the result is not perfect, it's OK. The transfer port tube is made from PEEK with a 0.168" internal diameter. Inside the thimble, there is a slightly elongated hole, oblong on the front half and more square on the rear, with an area equal to the 0.168" diameter. That oblong hole transitions from a 0.168" diameter bevel on the inlet side of the thimble, where it mates with the transfer port tube.
Here is the thimble and transfer port tube:
(http://www.scotthull.us/photos/Armada/IMG_2376.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2379.JPG)
I have an FX 20206 slug liner (not shown) that will be used in the barrel. The barrel system required some extra parts. The threaded end was made from a 3" long 1/2-20 setscrew. I ruined three drill bits before I realized how hard it was. I ended up annealing it in order to finish the machining. It will be bonded to the muzzle end of the liner. I printed a plastic stepped washer and a flange nut out of ABS. The nut is used to tension the barrel. I might switch to aluminum or steel later.
(http://www.scotthull.us/photos/Armada/IMG_2385.JPG)
The outer bushing will be bonded into the bored out breech block. The smaller tube will be bonded to the barrel liner and held into the bushing with the four setscrews:
(http://www.scotthull.us/photos/Armada/IMG_2386.JPG)
I left sufficient thread extension to attach a moderator, if I decide to do so:
(http://www.scotthull.us/photos/Armada/IMG_2392.JPG)
The back end of the assembly (minus the rifles liner):
(http://www.scotthull.us/photos/Armada/IMG_2393.JPG)
If this barrel system does not work out, I'l go to a heavy walled LW Polygon barrel. It would be a lot simpler than using a barrel liner that must be contained. The early decision to try a tensioned configuration added significant complexity.
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Lookin good scott .. way over my head electronics wise ... WAY over !
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The arduino can work in the single digit useconds.
I had considered a capacitor discharge similar to yours but I have most of the components for the arduino setup. I had to order the boost converter.
Either way should work the same so long as supply is regulated.
I am going to have to get a regulator setup. Without regulator, my way should drop fps with each shot.
I know yours is regulated but if it wasn’t, I assume yours would have the ability to ‘balance’ so to speak, since as the pressure drops, dwell will increase due to the closing force lessening and cap is able to hold at lower voltage. Would be curious if one could ‘tune’ your system with a rheostat across the solenoid to speed discharge rate of a larger cap? Now I’m rambling.
Thanks for the info
Dave
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The arduino can work in the single digit useconds.
I had considered a capacitor discharge similar to yours but I have most of the components for the arduino setup. I had to order the boost converter.
Either way should work the same so long as supply is regulated.
I am going to have to get a regulator setup. Without regulator, my way should drop fps with each shot.
I know yours is regulated but if it wasn’t, I assume yours would have the ability to ‘balance’ so to speak, since as the pressure drops, dwell will increase due to the closing force lessening and cap is able to hold at lower voltage. Would be curious if one could ‘tune’ your system with a rheostat across the solenoid to speed discharge rate of a larger cap? Now I’m rambling.
Thanks for the info
Dave
Even with the computer controlled mosfet, you will still need the large capacitors. Unless you use a HUGE boost converter. The current draw, though brief, is high. I'm using a small boost converter with the main concern being it's ability to replenish the capacitors in time for the next shot.
I did realize that it could be made to self regulate over a wide pressure range. A standard PCP can do the same. But even though the velocity can stay the same over a wide pressure range, the shot quality/sound/feel changes. And I don't like that. So I prefer a constant pressure regulator. Cost for a bottle regulator is low these days.
I can trim the boost converter to change it's output voltage. So I could can fine tune it without changing capacitors. The "cuttoff" will happen sooner with a lower voltage setting. For efficiency, I'd like to use a good percentage of the stored capacitor energy to keep the valve open. Any energy remaining in the capacitors after cutoff is wasted.
I am using a balanced valve that is easier to open on high pressure, but likes to close forcefully. A specially design balanced valve might be a compliment for use with an electronic actuator such as this project. Use near 1-to-1 balance, and only vent the balance chamber to atmosphere (like a dump valve), and then rely on a slightly heavier spring for most of the closing force. Probably a stronger spring on the plunger as well, in order to retract it faster.
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An Arduino may have microsecond resolution and 10 microsecond actuation for the pulse from the capacitors.... but what about the solenoid to open the valve?.... It still has to move a mass (the armature) in a controlled manner is an accurately controlled timeframe.... A 0.0001 sec. difference in dwell on a typical PCP like a Disco will cause about a 50 fps change in velocity.... You need to be able to control the valve dwell to within about 10 uSec. to equal the consistency of a mechanical hammer....
I'm not saying this can't be done, because I have NO experience with the type of electronics involved.... I'm just saying what we must be seeing now with our "knock-open" mechanical valves and spring driven hammers....
Bob
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Scott,
Yes, I’m aware I need a cap to feed from. I’ll use a little larger than needed so recharge time should be proportional to dwell time.
Bob,
I am not familiar with the consistency of solenoids. I do know the arduino is precise and the mosfet can produce a near perfect square wave with rise and fall times in nseconds.
Lots of this stuff is new to me. I am 50 now and have been hobby building powder propelled guns for quite some time. (From scratch not kits). Have not messed with electronic triggers because they are a no no with firearms.
Dave
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Like I said, no idea what the consistency and adjustability of a solenoid is.... just making the point of what is required for consistent velocity.... If you don't care about efficiency, then dumping a fixed volume and pressure of HPA would be the way to go.... You can have as much dwell as you want and it won't matter, once the pellet leaves the muzzle.... However, the FPE is limited by the valve volume and pressure, and once the valve volume is greater than 50% of the barrel volume the amount of air wasted is huge.... Even with a 50% valve volume, with a dump valve 1/3 of the air adds nothing to the velocity, as it is still in the valve when the pellet exits....
Bob
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Bob, I need to ask about something and you have had experience with - the tensioned barrel.
After researching it yesterday, I realize that I might have a problem with mine as-is. I'm using a carbon fiber shroud as the compression member. The CTE (coefficient of thermal expansion) is significantly less than steel, so tension will vary with temperature. I could switch the CF shroud for a steel shroud and that should solve that problem, but assuming I keep the CF shroud - I see that you have experimented with a belleville stack to provide a more constant tension. About 900lb? My .22 caliber tensioned liner is only .315" OD, for a cross sectional area of about .039 sqin. It will stretch about .02" under 900lb load. I'm thinking a load of about 250-500 lb of tension might be better in my case.
The current barrel end-piece has enough length for a 1/2" total stack of belleville washers as-is. More than that and I'll need to remake the end-piece. I'm going to try an elastomer spring first. I'm printing out a TPU (thermoplastic polyurethane) bushing to act as a spring. At least until I can get some thermoset polyurethane. I might order a poly die spring and cut it shorter. They typically allow for 15-25% compression, so a 1/2" tall spring would allow for .075-.125" compression. Over a 50 F range of temperature, the liner will expand about .01", so I'm thinking that about .05-.08" of compression at room temp might be good enough. That would result in a barrel tension of 300-600lb.
Your thoughts?
Edit: I just printed and tested a TPU bushing/spring. It is 1/2" ID x 7/8" OD x 0.5" long. The spring rate is 3000 lb/in. So it will provide about 300 lb. of tension load.
BTW - there will be a clear cover on the electronics, but as shown, there is no cover yet.
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FWIW ... I too have been tensioning barrels for a while now & found you don't need to be that elaborate. Tension tube must have very square ends against very square end cap and breech is all thats required.
Threaded barrel at muzzle or a slip on threaded air stripper ( Epoxied on or Sleeve retainer ) with the end tap being hand tensioned to only modest compression has been rock sold and trouble free.
Shroud tube best being steel, but aluminum is working too w/o issue.
JMO tho finding K.I.S.S. works just fine.
Scott S
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FWIW ... I too have been tensioning barrels for a while now & found you don't need to be that elaborate. Tension tube must have very square ends against very square end cap and breech is all thats required.
Threaded barrel at muzzle or a slip on threaded air stripper ( Epoxied on or Sleeve retainer ) with the end tap being hand tensioned to only modest compression has been rock sold and trouble free.
Shroud tube best being steel, but aluminum is working too w/o issue.
JMO tho finding K.I.S.S. works just fine.
Scott S
OK - it is simple enough as far as the breech end. I can include the elastomer spring without any extra work. Are you saying that no spring needed? And only moderate tension? Without a spring, and with only moderate tension - steel should be OK, but at low temps, the aluminum shroud will loosen, and the CF shroud will loosen at high temps. I'll try the elastomere spring and CF shroud for now, but will make a steel shroud later (probably 7/8" OD x .083" wall - end bored slightly).
JSAR uses an elastomere spring on the Raptor shroud - right? What is their shroud material? I assumed that it was aluminum.
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I would highly recommend the Bellevilles if the materials for the barrel and shroud don't have the same thermal coefficient of expansion.... For your barrel I would imagine you can use less tension.... Increase the tension until the groups tighten up, after that happens further tension usually does little....
Bob
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I would highly recommend the Bellevilles if the materials for the barrel and shroud don't have the same thermal coefficient of expansion.... For your barrel I would imagine you can use less tension.... Increase the tension until the groups tighten up, after that happens further tension usually does little....
Bob
In the space I have, I'll be working with about 1/8 max deflection when using the polymer spring. I can get whatever tension I want by increasing the diameter. The deflection is almost as much as I would get with the belleville washers. I'll test it with the poly spring and maybe get the bellevilles later if I want tension-consistency over an even greater temperature range.
A steel shroud is also an option that I'm considering even more.
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JSAR actually went away from the POLY compression sleeve & collars doing instead a machined length of Acetal with a Fat o-ring at each end running it in a groove next to barrel. The o-rings sits proud in the groove and upon tensioning the barrel the o-rings are nearly crushed square within there respective grooves. One being against receiver, other against a collar the shroud also butts into. Shrouds are aluminum, as are the threaded air stripper, tensioning part at muzzle.
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A crushed O-ring stack (with some movement still available, so acting like a stiff spring) sounds like a reasonable alternative to Bellevilles or a strong spring.... The problem with solid metal-to-metal (with different rates of expansion) is that a temperature change might cut your tension in half or double it with the kind of temperature change you might get under differing weather conditions.... It's just a matter of doing the math for the stretch/compression at one temperature and load.... and then figuring the length change at the other temperature and recalculating the load....
If your barrel is CrMoly and with that small a cross section you could use a very thin wall (under 1/32" ? ) CrMoly shroud.... just do a buckle calculation for it at the expected load....
Bob
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JSAR actually went away from the POLY compression sleeve & collars doing instead a machined length of Acetal with a Fat o-ring at each end running it in a groove next to barrel. The o-rings sits proud in the groove and upon tensioning the barrel the o-rings are nearly crushed square within there respective grooves. One being against receiver, other against a collar the shroud also butts into. Shrouds are aluminum, as are the threaded air stripper, tensioning part at muzzle.
The polys (TPU and Acetal) have a very high thermal expansion coefficient. Combine that in series with the low expansion of CF tubing, and it's not that far from steel. Aluminum instead of CF would be worse.
I think the CF + TPU will be a good combination. We'll see.
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JSAR actually went away from the POLY compression sleeve & collars doing instead a machined length of Acetal with a Fat o-ring at each end running it in a groove next to barrel. The o-rings sits proud in the groove and upon tensioning the barrel the o-rings are nearly crushed square within there respective grooves. One being against receiver, other against a collar the shroud also butts into. Shrouds are aluminum, as are the threaded air stripper, tensioning part at muzzle.
"...One being against receiver, other against a collar the shroud also butts into...."
Motorhead,
Whenever I look at the JSAR system, I wonder why the resilient member (poly spring/bushing) is against the receiver, between the breech and the shroud. That is the point of maximum bending stress. Why not put the spring at the muzzle? Any resilient member near the breech is going to act like a pin joint. I design so that I minimize any resiliency/movement between the scope and muzzle.
If I had a Raptor, I'd replace the aluminum shroud with CF and move the collar and poly spring to the muzzle end.
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A crushed O-ring stack (with some movement still available, so acting like a stiff spring) sounds like a reasonable alternative to Bellevilles or a strong spring.... The problem with solid metal-to-metal (with different rates of expansion) is that a temperature change might cut your tension in half or double it with the kind of temperature change you might get under differing weather conditions.... It's just a matter of doing the math for the stretch/compression at one temperature and load.... and then figuring the length change at the other temperature and recalculating the load....
If your barrel is CrMoly and with that small a cross section you could use a very thin wall (under 1/32" ? ) CrMoly shroud.... just do a buckle calculation for it at the expected load....
Bob
I did the math and it looks like a carbon fiber tube with a polyurethane spring could give me the lightest, stiffest shroud (compression member) while closely matching the thermal expansion of the steel barrel (tension member).
All steel (shroud, barrel, bellevilles) would also be equal in thermal expansion, but heavier and not as stiff.
The CTF of carbon fiber tubing can vary from slightly negative to slightly positive, with the aerospace grade as low as -1x10^-6 in/in F, and the commercial grade as high as 2x10^-6
Steel: 6.5x10^-6 in/in F
Carbon fiber: 2x10^-6 in/in F
Polyurethane A80: 180x10-6 in/in F
I'll have a 25.625" section of steel barrel in tension inside a 25" CF shroud and .625" long Poly spring.
barrel: 25.625 x 6.5x10^-6 = 0.000167 in/F
shroud + spring: (25 x 2x10^-6) + (0.625 x 180x10^-6) = 0.000163 in/F
That's a near perfect match.
The CF tube might have a lower CTF value than I used, and that could make for a larger difference, but the poly spring at 300 lb. of compression will have 1/8" of compression. So any difference of just a few thousandths of expansion will result in a low % change in tension. You stated that your experiments have shown a minimum tension for best accuracy, and greater than that changes nothing. If I take the tension slightly past that point, then the poly spring will maintain adequate tension even if there is a significant difference in expansion between the barrel and shroud.
Worst case, CTF of CF tube is negative, and temperature variation is large. A CF tube with a negative CTF of -1x10^-6 at 100 F temp variation will result in a .006" length difference between shroud and barrel. That is easily taken up by the poly spring which is slightly over tensioned.
Based on the numbers and my current design, I don't expect to have any issues with thermal expansion differences.
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Sounds like a good match....
Bob
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Your SOOOOOO over thinking it. Ya darn engineer !!!
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Your SOOOOOO over thinking it. Ya darn engineer !!!
At least put the spring on the muzzle end. Then the breech end of the shroud that we are so careful to square-up can be of some benefit.
Did you ever notice that many gun barrels are thicker at the breech. Several reasons for this, including - that's where they need to be stiffest to resist bending/droop/whip.
It does not make any sense to anchor the assembly at the breech through a flexible member. I'm curious to know why the Raptor is designed that way. Am I missing something - maybe I'm under-thinking it.
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At least put the spring on the muzzle end.
I agree 100%.... By putting the spring at the breech, you are creating a baseball stiff barrel and hinging it at the receiver.... ::)
Bob
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I agree too .. just not how it being done at JSAR. ( not my designs behind the gun ) My personal tensioned barrels have NO buffer or spring etc .. Square ends against square surfaces tighten up via a threaded barrel at muzzle or a glued on air stripper having the 1/2-20 threads & as you say baseball bat stiff !
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I finally got the whole gun together and did some chrony testing in the garage. FPE is close to what I want but the settings are not working as expected - higher hammer energy was often giving less FPE. Definitely NOT linear. I currently have a balanced valve in the gun and am suspecting that is the reason for the counter-intuitive behavior - more on that later.
I ran directly from the large plenum and recharged every 4 shots. I ran tests at both 2000psi and 3000psi. The plunger stroke is at maximum, and I'll need to disassemble the gun to try shorter stroke settings - more on that later. I also tried various voltage and capacitance settings. 3000psi produced more FPE but not by much. The end results showed that max power was achieved at much lower voltage and capacitance settings than I thought I would need. At low voltage settings, and capacitor setting 1, fps was anemic, but climbed very fast with any increase in settings - quickly peaked - and then dropped slightly if I went higher. I expected it to climb slowly and not peak.
This gun is a .22 and I tried both 25.39gr and 34gr. Here are the maximum performance values I got from the various settings tried:
3000psi
25.39gr - 1118fps (70fpe) capacitor setting 3
34gr - 1019fps (78fpe) capacitor setting 2
2000psi
25.39gr - 1025fps (59fpe) setting 2
Looking at the design of the balanced valve, here are my suspicions: The balance chamber vent is down stream of the poppet. As the poppet opens more, poppet area eventually matches the transfer port area, the balance chamber is fully pressurized and no longer assists in holding the valve open. So the valve then closes quickly. If the poppet were to be restricted from opening some, the valve would not want to close so fast. But more caps should be able to resist the closing. Maybe too much hammer/plunger energy is causing the plunger to bounce? Nothing is certain at this point. The next thing I'll try is to reduce the plunger stroke and see if I get a linear FPE increase. And if not, I'll swap the standard valve back in and try that.
The 3000psi regulator that came in was wrong, so I assembled the bottle with the 2000psi regulator and that's what I'll use for now. A little lower peak FPE but more shots.
The circuitry is working OK for testing but I have some small changes planned.
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How fast most balanced valves close is a function of how quickly the balance chamber pressure rises to the throat pressure.... The smaller the balance chamber volume and the larger the vent hole into the throat, the more rapidly that occurs.... and the more the valve acts like a conventional valve that is easy to knock open initially.... I don't know if that applies to your design or not....
If the plunger strikes the back of the valve body, it can bounce off it.... and the more energy you put into it, the faster the rebound and the less the valve dwell.... If you have a much longer valve stem, so that the dwell is proportional to "hammer" strike without bottoming out.... it will be much more conventional to tune....
Bob
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as i recall the hammer is the stem , No ?? in other words there is no striking taking place.. Just pushing against the poppet back pressure.. Anyway ,good numbers, depending on the balanced design , the poppet in the far forward position can cause a choke point , where gains would be lost ( ive built one like this and it took me a minute ( read 3 days ) to figure that out ..
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How fast most balanced valves close is a function of how quickly the balance chamber pressure rises to the throat pressure.... The smaller the balance chamber volume and the larger the vent hole into the throat, the more rapidly that occurs.... and the more the valve acts like a conventional valve that is easy to knock open initially.... I don't know if that applies to your design or not....
If the plunger strikes the back of the valve body, it can bounce off it.... and the more energy you put into it, the faster the rebound and the less the valve dwell.... If you have a much longer valve stem, so that the dwell is proportional to "hammer" strike without bottoming out.... it will be much more conventional to tune....
Bob
Valve stem projects 0.165" from valve body. I'll try cutting the plunger/hammer stroke in half as that is still sufficient to open the valve, and maybe it won't bounce so much (if that is what it's doing). I can probably bump up the voltage to max to hopefully hold the valve open longer.
With the short stem, any excess kinetic energy in the hammer is being wasted. Better to contact the valve sooner, valve opens slower, but more charge remaining to delay valve closing.
One drawback of the Armada vs Marauder is that there is no access to the hammer adjuster without taking the action out, and that too is more involved on the Armada. Until I get the stroke satisfactory, I'll test it with the action separate from the stock. I have some ideas about how to modify the Armada stock to allow for hammer adjustment - probably later.
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as i recall the hammer is the stem , No ?? in other words there is no striking taking place.. Just pushing against the poppet back pressure.. Anyway ,good numbers, depending on the balanced design , the poppet in the far forward position can cause a choke point , where gains would be lost ( ive built one like this and it took me a minute ( read 3 days ) to figure that out ..
No. The solenoid plunger acts as a hammer. It weighs about 33 grams. Currently set at 1/2" stroke. But I can use a lot shorter stroke and still fully open the valve. So that's what I'll try next.
It's much like a conventional hammer except that instead of using a spring, I use a solenoid to launch the plunger/hammer. By adding capacitor charge instead of adding hammer mass, I'm attempting to apply force against the stem a little longer to hold the valve open longer. The longer dwell time is what is needed for heavier projectiles.
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If the plunger stroke is fixed (eg. currently 1/2") is it hitting a stop inside the solenoid?.... If so, the plunger would be bouncing off the end of the solenoid, not the back of the valve.... How do you adjust the stroke of the plunger, by changing it's location relative to the valve stem?.... If that is the case, then the plunger would be bouncing off the valve body, no?....
You are certainly working with a much different tuning situation than a conventional hammer, where the lift is governed by the hammer being slowed by the valve opening, and the lift limited by when the valve closing force overcomes the hammer momentum.... The hammer should never it the back of the valve, except when an adjustable resilient buffer is being used (which complicates tuning)....
Remember, in a hammer, energy determines lift and momentum determines dwell.... Also, energy comes from the average spring force times the hammer travel (independent of hammer mass)…. However, for a given hammer mass and energy, the resulting hammer velocity (at the instant the valve cracks) determines the residual momentum, so changing the hammer mass changes the relationship of residual energy to residual momentum....
You may have a much different dynamic, because your energy is supplied by the discharge of the capacitor.... I would think the momentum of the plunger (and therefore valve dwell) would still vary according to the mass of it.... even if the energy (discharge) remains the same....
Bob
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Bob,
To reduce the stroke, the plunger starting position is moved closer to the stem. The plunger has a snap ring and nylon stop washer on the tail end. That limits the amount of travel. The nylon washer bottoms out at the tail end just before the front of the plunger bottoms out in solenoid, and that is just before the stem is near max compression. Any bouncing would be off the nylon washer.
I have a 3/8" setscrew in the back of the rear tube cap that can push the plunger further in against it's return spring. That reduces the plunger/hammer stroke.
The plunger does act as a standard kinetic hammer. For a given stroke, hammer energy increases greatly for a higher voltage (voltage squared) and slightly for a higher capacitance. In addition to giving momentum to the plunger, any remaining charge in the capacitors applies a force against the valve stem. For a duration in the low millisecond range. More capacitance extends the duration of that force. Higher voltage increases the magnitude of that force.
My plans for the next round of testing will be to use maximum voltage, and minimum stroke, with just enough plunger momentum to open the valve. And then use additional capacitance to extend the dwell when desired.
At least that's what I'm trying to do.
Edit: I measured the actual stroke and travel of the assembled gun. Plunger/hammer stroke is 0.42" before it contacts the valve stem. And then it travels another 0.10" before the solenoid hits it's nylon stop washer. So the valve opens 0.1". That should be enough peripheral area to get full flow through the 0.25" dia throat . Now the trick will be to see if I can use increased solenoid energy/duration to keep the valve open. So far, it's not happening. Goal - pop the valve open to 0.1", and hold it open as long as needed for the desired FPE.
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I retested today with the hammer stroke reduced to about 0.15" and got better results though shot to shot consistency is horrible (+/- 3%)velocity.
I tested at 2000psi with 25.39gr. This is about what I'm getting,
(switch setting #), fps, fpe:
(1) 559fps 18fpe
(2) 841fps 40fpe
(3) 992 fps 55fpe
(4)1012fpe 58fpe
If I run the hammer stroke up more than about 0.15", I start to see reduced fps at higher switch settings. Small changes in stroke seem to make outsized changes in velocity.
The balanced valve seems to be a touchy element in the mix (though it makes it easy to coax high FPE).
I'm going to install the factory Armada valve until I can get the circuitry figured out/dialed-in. Factory port size is a little over 0.14", so I expect to lose maybe 30fps on the high end. I can bore iy out later if I feel the need.
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I will be interested to see the results. I am wondering how well the solenoid can crack a factory valve open compared to a balanced. Once opened, is a factory valve easier to hold open?
I have my arduino programmed, got a boost reg and a premounted fet with driver and a 9v solenoid. Just need some shop time to put it together and get the circuit working.
Your results so far are interesting. It seems to me you have proved the concept now you just need to work out the kinks.
Dave
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I installed the factory Armada valve and the first thing I noted was that performance at 2000psi was anemic. Valve lock. The 33g gram hammer/plunger and 33v solenoid is inadequate in it's current form. I reduced the pressure to 1800psi and it got better so I tested at 1500psi which was even better. But nowhere near the FPE of the balanced valve. It performed in a fairly linear manner which was good, but the FPE was pretty close to a standard Armada/Marauder, which I guess is to expected since the valve currently installed is the unmodified factory valve.
1500psi, 18.1gr
(1) 589fps 13.9fpe
(2) 802fps 25.9fpe
(3) 876fps 30.9fpe
(4) 899fps 32.5fpe
1500psi, 25.39gr
(1) 473fps 12.6fpe
(2) 690fps 26.9fpe
(3) 755fps 32.2fpe
(4) 790fps 35.2fpe
The factory valve has .25" of stem travel, and I setup the stroke to fully utilize the .25" if needed, so I doubt that I ever bottomed it out. But it's performance is nothing to get excited about. Great trigger, easily switched FPE output from 12 up to 35fpe. Super shot count. Nothing wrong with all that, and certainly adequate for the 18.1gr, but my intent is to shoot 25.39gr and 34gr pellets (and slugs at a later date).
So, for now, that means going back to the balanced valve, learn more about the design, and figure out it's idiosyncrasies. My original thinking was to hold the valve open against a stop using the solenoid and additional capacitance. Now I'm leaning toward allowing plenty of overtravel and using the additional switch settings to increase the kinetic energy of the plunger. My next step will be to set the current balanced valve up so that I use it's full .15" stroke (I only used .10" in the first tests). That's for tomorrow. If it improves things, I'll look into remaking the valve with a longer stroke so as not to bottom it out ever, if possible.
Edit: The balanced valve is by Motorhead. I took it apart. Clean and simple design. Motorhead mentioned cutting the poppet face back to increase the travel and stem projection. Now I see how it's done.
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I will be interested to see the results. I am wondering how well the solenoid can crack a factory valve open compared to a balanced. Once opened, is a factory valve easier to hold open?
I have my arduino programmed, got a boost reg and a premounted fet with driver and a 9v solenoid. Just need some shop time to put it together and get the circuit working.
Your results so far are interesting. It seems to me you have proved the concept now you just need to work out the kinks.
Dave
The balanced valve is a lot easier to open at higher pressures. At low pressures, it's probably not really needed. Neither valve is easy hold open, though there are probably design avenues available in the balanced valve to make it easier to hold open longer. After recent tests, I'm thinking of more travel (kinetic energy), rather than try to hold it open in a stationary position.
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I will be interested to see the results. I am wondering how well the solenoid can crack a factory valve open compared to a balanced. Once opened, is a factory valve easier to hold open?
I have my arduino programmed, got a boost reg and a premounted fet with driver and a 9v solenoid. Just need some shop time to put it together and get the circuit working.
Your results so far are interesting. It seems to me you have proved the concept now you just need to work out the kinks.
Dave
The balanced valve is a lot easier to open at higher pressures. At low pressures, it's probably not really needed. Neither valve is easy hold open, though there are probably design avenues available in the balanced valve to make it easier to hold open longer. After recent tests, I'm thinking of more travel (kinetic energy), rather than try to hold it open in a stationary position.
REDUCE the bleed hole size feeding the balance chamber. Slower the chamber pressurizes more the valve will have a trend to hang open and continue flowing air. This along with transfer path restriction become more interwoven into what weight projectile / caliber the gun in use actually is. If shooting heavy projectiles, tight fitting etc the pressure within throat & transfer path sticks around longer ( more duration ) and if wanting long drell you likely should chamber vent smaller.
If on the other hand your shooting lighter & quicker to exit projectiles the duration pressure is within the throat & transfer path will be shorter, if you want the valve to close faster you chamber vent larger.
While these balanced valves are a good work around for Easy Opening and high power, there is attributes and deficits you should be familiar with and build the valve parts more specialized to the use requirements.
Just sharing thoughts ... as you were sir ;)
Scott S
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So here is my thinking and please correct if wrong.
In a spring driven hammer system, at any given time (save when poppet changes direction), everything is dynamic. Nothing stays static. As such, the poppet would need ‘room to move’ so dwell can be changed. At some point, the poppet opens to ‘full flow’. The rest of the ‘opening of poppet’ is just eating time to create dwell.
In solenoid operation, the closer the ‘hammer’ is to full stroke, the greater it’s power. So if we knew the point at which the poppet was as close to ‘full flow’, the solenoid would benefit by only opening/holding to that point. For example, if full flow was achieved at .080” lift, the solenoid would be strongest to let it hit the poppet with only .080” of stroke left. Plus, it would allow the hammer some momentum to build for the initial cracking.
So for a given seat passage diameter, is full flow achieved raising the poppet just enough to equal the area of the passage diameter? I understand turbulence will have effect, but would that be close?
Dave
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At some point, the poppet opens to ‘full flow’. The rest of the ‘opening of poppet’ is just eating time to create dwell.
Exactly correct.... Full flow rate occurs when the lift is 1/4 the throat diameter (eg. 1/16" on a 1/4" throat)…. After that, you are getting more physical lift, and hence more dwell, but the flow rate does not increase further.... This is because the "curtain area" (area under the perimeter of the seat) equals the throat area at that lift....
Area of perimeter = D x PI x L
Area of throat = D x D x PI / 4
When those are equal, D x PI x L = D x D x PI / 4 …. Cancelling out we are left with L = D / 4
The flow rate may peak when the lift is slightly greater than that.... but on the other hand there is a reduction in the throat area from the area of the stem working the other way.... Therefore using L = D / 4, with the D being the ID of the throat is the best prediction of the lift giving full flow rate....
If the solenoid has the ability to maintain that lift through the discharge of the capacitor, then holding at that lift may be the best use of the energy.... particularly if, as I understand solenoids, the force is the greatest when the armature is fully inside the coil (ie full armature travel)…. This should also give the maximum cracking force when the plunger contacts the stem, as the armature will be the furthest inside the coil possible while still delivering the required lift....
Bob
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This is the force curve for the solenoid linked to earlier in this thread.
Dave
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So here is my thinking and please correct if wrong.
In a spring driven hammer system, at any given time (save when poppet changes direction), everything is dynamic. Nothing stays static. As such, the poppet would need ‘room to move’ so dwell can be changed. At some point, the poppet opens to ‘full flow’. The rest of the ‘opening of poppet’ is just eating time to create dwell.
In solenoid operation, the closer the ‘hammer’ is to full stroke, the greater it’s power. So if we knew the point at which the poppet was as close to ‘full flow’, the solenoid would benefit by only opening/holding to that point. For example, if full flow was achieved at .080” lift, the solenoid would be strongest to let it hit the poppet with only .080” of stroke left. Plus, it would allow the hammer some momentum to build for the initial cracking.
So for a given seat passage diameter, is full flow achieved raising the poppet just enough to equal the area of the passage diameter? I understand turbulence will have effect, but would that be close?
Dave
"...the closer the ‘hammer’ is to full stroke, the greater it’s power..."
Power is a function of voltage. Kinetic energy (not power) would be highest after the plunger accelerates over it's full stroke. Force would be highest at the very end of the stoke (assuming the voltage was constant - but it's not).
Most of your comments express exactly what I have been thinking. Pop the valve open just enough for full flow, and then hold it (dwell) long enough to get the desired FPE for the current pellet. So far I have not been able to do that. Maybe I don't really have adequate static force to hold the valve open? Maybe I need more voltage?
At 2000psi, I can get by with a short plunger stroke to crack the valve (probably about .16" free stroke ). The short acceleration distance/time leaves the residual voltage in the caps highest, which is what I need to keep the valve open.
Same for valve travel. Use minimal as possible for optimal flow.
At minimum, the curtain area needs to match the port area. That's a very small valve opening.
I've been setting up excess margin of travel in both the stroke travel and valve travel. I guess I should minimize both as that will maximize my holding force. And if that doesn't work, figure out how to raise the voltage increase the holding force even more.
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At some point, the poppet opens to ‘full flow’. The rest of the ‘opening of poppet’ is just eating time to create dwell.
Exactly correct.... Full flow rate occurs when the lift is 1/4 the throat diameter (eg. 1/16" on a 1/4" throat)…. After that, you are getting more physical lift, and hence more dwell, but the flow rate does not increase further.... This is because the "curtain area" (area under the perimeter of the seat) equals the throat area at that lift....
Area of perimeter = D x PI x L
Area of throat = D x D x PI / 4
When those are equal, D x PI x L = D x D x PI / 4 …. Cancelling out we are left with L = D / 4
The flow rate may peak when the lift is slightly greater than that.... but on the other hand there is a reduction in the throat area from the area of the stem working the other way.... Therefore using L = D / 4, with the D being the ID of the throat is the best prediction of the lift giving full flow rate....
If the solenoid has the ability to maintain that lift through the discharge of the capacitor, then holding at that lift may be the best use of the energy.... particularly if, as I understand solenoids, the force is the greatest when the armature is fully inside the coil (ie full armature travel)…. This should also give the maximum cracking force when the plunger contacts the stem, as the armature will be the furthest inside the coil possible while still delivering the required lift....
Bob
We are all on the same page as far as how it SHOULD work.
Ideally, the solenoid could crack the valve without having any free stroke. I can't do that now. At least not at 2000psi. The cracking force still depends on the armature inertia. Maybe a balanced valve with a bigger diameter balance piston.
Wouldn't the minimum curtain area only need to equal the minimum flow area (the transfer port). In my case the transfer port area is less than the throat area.
That gives me another thought - by using an even smaller curtain area, we would get a pressure drop across the throat. So the stem vent would see a pressure reduction, resulting in a lower pressure in the balance chamber. Would this make it easier to keep the valve open? Maybe. Except that the if the poppet face gets too close, that pressure differential and flow also might act to drag the valve closed.
OK - I've got more things to try.
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I like to see the throat area (ID area less stem area) about 10-20% greater than the exhaust/transfer/barrel port area.... That allows for the flow loss around the stem.... Then when figuring the lift for maximum flow, I use the throat ID / 4.... It may not be right, but I feel doing it that way makes the throat and lift "big enough" to allow maximum port flow....
IMO, you only get a significant pressure drop across the poppet towards the end of the shot cycle, when the pellet velocity is high.... When the valve is just opening, the pellet is essentially stationary, and the pressure rise in the throat occurs very quickly, and to nearly reservoir pressure.... This occurs very early in the opening stage, when the poppet is only a few thou off the seat....
Bob
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I like to see the throat area (ID area less stem area) about 10-20% greater than the exhaust/transfer/barrel port area.... That allows for the flow loss around the stem.... Then when figuring the lift for maximum flow, I use the throat ID / 4.... It may not be right, but I feel doing it that way makes the throat and lift "big enough" to allow maximum port flow....
IMO, you only get a significant pressure drop across the poppet towards the end of the shot cycle, when the pellet velocity is high.... When the valve is just opening, the pellet is essentially stationary, and the pressure rise in the throat occurs very quickly, and to nearly reservoir pressure.... This occurs very early in the opening stage, when the poppet is only a few thou off the seat....
Bob
OK - that would be true about the pressure drop only at higher flow rates (higher velocity, later in the shot cycle).
Earlier, I had gotten the switched capacitor banks to increase FPE with each switch setting. But that was with the factory valve. And the factory valve is not giving me the easy valve opening and high FPE that I wanted. With the balanced valve, there may be too many interrelated dependencies and I cannot predict what will happen when I switch capacitors up. So until I decide to investigate it more, I'm going to go with one capacitor and use other adjustments to change FPE. With the balanced valve and >2000psi, I can shoot the .22 JSB 25.39gr at 1030+ fps (60fpe), and that was my primary goal. Later I'll redesign the electronics box to be smaller (fewer capacitors and fewer switches).
I think you can get away with just changing the hammer strike on a standard valve when wanting to change the FPE some. Maybe not with the balanced valve. Actually, that's not a great way to tune, but I thought that the electronic valve would give me more control over the dwell and might be all I need to change. Maybe an actual timer circuit would work (and a computer control?).
I'm keeping the electronic striker, but doing away with the multiple switched capacitors for now. I already went through 1-1/2 tins of pellets just testing various settings over the chronograph (spent most of today). It's time to finish that up and get it out to the range.
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I settled on a tune for now, and did some final chrony testing before I shoot some targets (probably on Thursday since rain is predicted for tomorrow). I'm getting some blow-by around the thimble and breech. It could be the thimble o-ring, but I suspect it's the transfer port tube. It's made 100% from PEEK with no o-rings. I probably need to give it a few more thousandths of crush length in order to get it to seal. It's not too bad, so I'm not going to tear down yet to fix that.
regulator pressure - 2000psi
armature/plunger/hammer mass - 33 grams
armature/plunger/hammer stroke - 0.42"
voltage peak - 35v
capacitance - 7500uf
JSB 25.39gr
fps, FPE
1008, 57.3
1009, 57.4
1011, 57.6
1006, 57.1
1011, 57.6
Avg: 1009
SD: 1.9
FPE: 57.4
Nielsen 27gr 0.217"
fps, FPE
946, 53.7
971, 56.5
964, 55.7
961, 55.4
966, 56.0
Avg: 962
SD: 8.5
FPE: 55.5
JSB 34gr
fps, FPE
886, 59.3
878, 58.2
890, 59.8
868, 56.9
885, 59.2
Avg: 881
SD: 7.7
FPE: 58.7
That's only five shots each, so the SD may not be all that precise. After shooting hundreds over the chrony last week, I need to conserve pellets for target testing. I was going to get a .22 Raptor and tune to a little under 60fpe. I think this Armada will be a good substitute. If I want to shoot heavier slugs later, I'm guessing I can get about 80fpe at 3000+psi.
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It appears the consistency has significantly improved. How far open is the poppet at full ‘lock up’?
Dave
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It appears the consistency has significantly improved. How far open is the poppet at full ‘lock up’?
Dave
Currently, when plunger bottoms out, popper is open 0.08”. I could lengthen the plunger and increase that up to 0.15”, since that is how far the stem projects from the valve face. But doing so did not improve FPE any significant amount.
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I did some target shooting today. Accuracy was all over the place at 30 yards so I moved in to 22yds to stay on paper. Still bad until I noticed plastic chipping away from the edge of the 3D printed moderator. It was clipping pellets. I drilled it out to 0.37" and things got better. Though the 25.39gr (old and new) were not great. The 34gr JSB is the only one that looked promising. At 60fpe, it's really too loud for the back yard so I ended up turning it down and trying lower FPE. At 700fps, the 34gr was shooting good. The 34gr is the only one that won't fit the magazines, so I was loading with tweezers. I'll make a single shot tray for it. And then I'll need to do more longer range/higher FPE testing at the range. Transfer port still has blow-by.
I did find out that if I shoot with a high frequency, velocity falls off. It could be regulator creep, but I think that the solenoid might be getting hot. It's mounted inside a plastic bushing inside the steel main tube. I'll likely make an aluminum bushing that thermally conducts from the solenoid to the main tube.
If I increase the capacitance any more, velocity drops. Raising voltage seems to do better. I raised the capacitor voltage from 35 to 38v (not really safe for a 35v capacitor). Not much difference in the FPE. Here is another ten shot string with the JSB 34gr at 38v:
JSB 34gr
fps, FPE
885, 59.2
896, 60.6
885, 59.2
881, 58.6
880, 58.5
888, 59.6
895, 60.5
891, 60.0
876, 58.0
893, 60.2
Avg: 887
SD: 6.4
FPE: 59.4
I'm leaning toward the 34gr at this point, though I have need more data.
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when i built my electric 2240 trigger group ( seen here https://www.youtube.com/watch?v=mgTel7tyzZg (https://www.youtube.com/watch?v=mgTel7tyzZg))
I noticed the same thing.. I thought My battery was dying , so to eliminate that variable i hooked up a large AH battery of the same voltage and did repeated tests.. it was the solenoid producing less energy ..I also ran a series of tests, more available current vs higher voltage and tried to seperate these with common sense.. Voltage was king which was odd since i always correlate amps with torque
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Raising capacitance and not gaining velocity indicates it’s not bottoming in the solenoid and holding as designed to do.
It seems like it’s still acting like a traditional hammer. That would explain why increasing voltage (the only variable you can change to increase amp draw) gives it a harder ‘throw’. For the record, changing the resistance in the coil is a variable that would increase amp draw but not easily done here.
Of course with use, it will heat up (as mentioned) and resistance will increase which will lower amp draw. This would also explain that lowering in velocity.
I only think that may be what is happening. I’m nowhere near an electrical engineer. :o
Dave
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Do you have an oscilloscope? You could measure both the voltage and current in the solenoid. You might consider a position sensor so you could tell the position of the poppet in the valve. I don't know if you have already done that. Once you know the valve state vs. time it might be easy to understand how to control it better. My apologies if you know this already.
A classic solenoid problem is 1) It's not fast enough, and 2) It consumes too much power. For faster pull in you need higher voltages. But higher voltages greatly increase power dissipation. This problem can be addressed using a peak and hold driver. They are commonly used for low impedance fuel injectors. Peak and hold drivers supply a good slug of current in the beginning and then reduce the hold current in the coil to reduce power dissipation.
It does sound like you are making pretty good progress. I'm watching as I find this amalgam of electronics, mechanics and air fascinating.
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Raising capacitance and not gaining velocity indicates it’s not bottoming in the solenoid and holding as designed to do.
It seems like it’s still acting like a traditional hammer. That would explain why increasing voltage (the only variable you can change to increase amp draw) gives it a harder ‘throw’. For the record, changing the resistance in the coil is a variable that would increase amp draw but not easily done here.
Of course with use, it will heat up (as mentioned) and resistance will increase which will lower amp draw. This would also explain that lowering in velocity.
I only think that may be what is happening. I’m nowhere near an electrical engineer. :o
Dave
You could be right. With the added capacitance, it should hold for a couple milliseconds before the capacitor voltage and solenoid holding force decays sufficiently to release, but it does not appear to be doing so. The power consumption goes up greatly if I apply too much, and the return is minimal. I'm probably going to go back to "flinging" the armature, and not try to hold the valve open with solenoid force. I can easily vary the impulse by adjusting the voltage output of the boost converter. That gives the same affect as more/less spring energy on a conventional hammer.
The first target tests show most promise with the heavier 34gr pellets so I now want to get the FPE up closer to 80fpe. I have gotten close to that using 3000psi in the plenum. The 3000psi regulator never came in (ordered from China) so I just ordered a 2800psi regulator from a USA shipper. Rather than control the both hammer energy and dwell electronically, I'll launch the hammer electronically, but vary dwell by adding armature/hammer mass. That is simple/proven method.
I have a few things on order that won't be in for a week or so. I'll spend next week cleaning up the design and working on the more compact circuit box.
I'm a mechanical engineer, and I too am nowhere near an electrical/electronics engineer.
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Do you have an oscilloscope? You could measure both the voltage and current in the solenoid. You might consider a position sensor so you could tell the position of the poppet in the valve. I don't know if you have already done that. Once you know the valve state vs. time it might be easy to understand how to control it better. My apologies if you know this already.
A classic solenoid problem is 1) It's not fast enough, and 2) It consumes too much power. For faster pull in you need higher voltages. But higher voltages greatly increase power dissipation. This problem can be addressed using a peak and hold driver. They are commonly used for low impedance fuel injectors. Peak and hold drivers supply a good slug of current in the beginning and then reduce the hold current in the coil to reduce power dissipation.
It does sound like you are making pretty good progress. I'm watching as I find this amalgam of electronics, mechanics and air fascinating.
I have an old scope, but not well versed on it's usage. All those classic solenoid problems exist big time. Holding force requirement too high, so power consumption too high, so too much heat, etc. My peak and hold is based on the time constant of the capacitor bank. It probably needs a digital control (or maybe a very big solenoid system?) in order to work consistently. If the solenoid is just used to accelerate the hammer, then it simplifies electrical design parameters.
I'm aware of the pulsed circuitry for overcoming some of the problems. But I would have a lot to learn to do that. I wanted to do it analog with a simple circuit, but as of now I can't, so time to try other things.
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I have enjoyed your testing so far and thank you for sharing your work.
I am still going to try it out with the processor control (Arduino). It will take me awhile I am sure.
I will start a thread on it and welcome your input there.
I'm sure your aware that you could use an rc timer to control a mosfet (ability to turn off). Just have the timer part be a controller and not part of the work side. Then you could use a very large cap for supply to keep power level at max longer. That would keep it analog.
Thanks again,
Dave
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Speculating that I might benefit from additional hammer mass, I modified a plunger to accept different weights. First thing is to compare performance with 43g total plunger mass to the original 33g plunger mass. I can also change the tip length as I used low strength purple loctite. I used brass for the weights as it will not develop residual magnetism. I have a rod of silicon-iron coming in that I can use later.
The next test will have:
43g hammer/plunger
0.42" total plunger travel
0.27" free travel
0.15" valve lift at full travel.
(http://www.scotthull.us/photos/Armada/solenoid-plunger-00.jpg)
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I wound a coil that is as close to the one you are using. I still need to make the plunger and armature.
Where did you source your silicon iron?
Dave
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I wound a coil that is as close to the one you are using. I still need to make the plunger and armature.
Where did you source your silicon iron?
Dave
https://www.ebay.com/sch/i.html?_nkw=silicon+iron+b+fm (https://www.ebay.com/sch/i.html?_nkw=silicon+iron+b+fm)
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As you add more mass (and springs) to the system, it will behave more and more like a traditional airgun valve system. I think it will be less tunable electrically, and more tunable mechanically. My original thought was you were trying to make an electronic valve. Is this no longer the case? Or is it more of running up against a problem that is proving difficult to solve? I applaud your efforts so far. If I had your talents, I'd be tempted to try this.
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As you add more mass (and springs) to the system, it will behave more and more like a traditional airgun valve system. I think it will be less tunable electrically, and more tunable mechanically. My original thought was you were trying to make an electronic valve. Is this no longer the case? Or is it more of running up against a problem that is proving difficult to solve? I applaud your efforts so far. If I had your talents, I'd be tempted to try this.
You are exactly right.
Knocking the valve open with a spring and mass uses kinetic energy.
Knocking the valve open with an electronic actuator (solenoid) is doable. It also uses kinetic energy.
A lightweight hammer has certain advantages. But for a high FPE airgun, with relatively heavy projectiles, the hammer usually needs sufficient mass to dwell the valve for a longer time period. My desire was to retain the light hammer, and extend the dwell by holding the valve open via solenoid force.
Maintaining enough force to hold the valve open, and control that time - that is proving to be the difficult part.
An alternative is to use a sufficient mass in the plunger for the heaviest projectiles. Though it is now more like a traditional knock open valve, I can control the kinetic energy electronically. I tune it with the trim pot on the boost converter. Since this alternative uses only one capacitor, I don't need the large capacitor bank, and I can make the control box more compact.
Still awaiting some components, so yet to see how successful. I now want at least 80fpe.
(http://www.scotthull.us/photos/Armada/IMG_2436.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2432.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2434.JPG)
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Scott,
As I had mentioned quite a few posts ago ..... If wanting valve to dwell longer ( Given a specific weight hammer capable of opening valve far enough ) Which I've proven time and time again can be done with fairly light hammer mass.
REDUCE the BLEED Hole size into the balance chamber. This will create more lag time in getting the closing force of the balance chamber becoming pressurized and exerting that extra push that helps push the poppet back to seat.
Wish to experiment ? Take out the valve, remove poppet and place a short piece of heat shrink on stem covering the vent hole to chamber ... reassemble & test. This will show you the other end of the closing speed spectrum having no balance chamber help what so ever ..... Watch what your dwell does then !!!
Scott S
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Scott,
As I had mentioned quite a few posts ago ..... If wanting valve to dwell longer ( Given a specific weight hammer capable of opening valve far enough ) Which I've proven time and time again can be done with fairly light hammer mass.
REDUCE the BLEED Hole size into the balance chamber. This will create more lag time in getting the closing force of the balance chamber becoming pressurized and exerting that extra push that helps push the poppet back to seat.
Wish to experiment ? Take out the valve, remove poppet and place a short piece of heat shrink on stem covering the vent hole to chamber ... reassemble & test. This will show you the other end of the closing speed spectrum having no balance chamber help what so ever ..... Watch what your dwell does then !!!
Scott S
I might try to reduce the bleed hole size at some point. My thinking why not to do it is that, even though it might give me more valve dwell, I might then have less control over the valve dwell - i.e., it might be more touchy to tune, especially for lower FPE.
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Scott,
As I had mentioned quite a few posts ago ..... If wanting valve to dwell longer ( Given a specific weight hammer capable of opening valve far enough ) Which I've proven time and time again can be done with fairly light hammer mass.
REDUCE the BLEED Hole size into the balance chamber. This will create more lag time in getting the closing force of the balance chamber becoming pressurized and exerting that extra push that helps push the poppet back to seat.
Wish to experiment ? Take out the valve, remove poppet and place a short piece of heat shrink on stem covering the vent hole to chamber ... reassemble & test. This will show you the other end of the closing speed spectrum having no balance chamber help what so ever ..... Watch what your dwell does then !!!
Scott S
I might try to reduce the bleed hole size at some point. My thinking why not to do it is that, even though it might give me more valve dwell, I might then have less control over the valve dwell - i.e., it might be more touchy to tune, especially for lower FPE.
Yes it would be ... Similar effect would be if you increased the chambers size relative to poppets primary diameter. that situation the valve would crack open easier yet and you would have a very touchy valve that would change power on a whim of pressure change or strike energy applied.
Another option is to decrease the balance chamber diameter which will add more general stability tho be harder to open.
A man just can't get no free lunch !!
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Scott,
As I had mentioned quite a few posts ago ..... If wanting valve to dwell longer ( Given a specific weight hammer capable of opening valve far enough ) Which I've proven time and time again can be done with fairly light hammer mass.
REDUCE the BLEED Hole size into the balance chamber. This will create more lag time in getting the closing force of the balance chamber becoming pressurized and exerting that extra push that helps push the poppet back to seat.
Wish to experiment ? Take out the valve, remove poppet and place a short piece of heat shrink on stem covering the vent hole to chamber ... reassemble & test. This will show you the other end of the closing speed spectrum having no balance chamber help what so ever ..... Watch what your dwell does then !!!
Scott S
I might try to reduce the bleed hole size at some point. My thinking why not to do it is that, even though it might give me more valve dwell, I might then have less control over the valve dwell - i.e., it might be more touchy to tune, especially for lower FPE.
Yes it would be ... Similar effect would be if you increased the chambers size relative to poppets primary diameter. that situation the valve would crack open easier yet and you would have a very touchy valve that would change power on a whim of pressure change or strike energy applied.
Another option is to decrease the balance chamber diameter which will add more general stability tho be harder to open.
A man just can't get no free lunch !!
Rather than trying to control dwell outside the valve via the hammer, maybe have a finely adjustable bleed port...
(http://www.scotthull.us/photos/Armada/valve-balanced-00.jpg)
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I believe the Slayer uses an adjustable bleed screw on the vent for the balance chamber.... Their valve is quite different, however, more like Lloyd Sikes original balanced valve, with the balance piston in the middle of the stem (using a 2-piece stem, pressed together, IIRC)…. Tom found the size of the vent critical, so he just made it adjustable....
Bob
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I'm liking that !!!
More screws to fiddle with is Good !!! ... actually NOT :P tho if it gets us where we need to be easier, sign me up !
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I'm liking that !!!
More screws to fiddle with is Good !!! ... actually NOT :P tho if it gets us where we need to be easier, sign me up !
Just thinking here -
It could make tuning easier. Less to fiddle with. Forget the buffer - it's a bandaid.
Use a very low mass hammer.
With the bleed adjuster all the way out, adjust the hammer energy (spring force or solenoid voltage) for 12fpe with light pellets (or whatever we want the low end to be).
With the bleed adjuster almost all the way in, we will get maximum FPE for the given pressure with heaviest pellets.
Once pressure and hammer spring is set, we would only adjust the bleed screw to adjust for different pellets or velocities.
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Now to find a way to do so without manufacturing an overly complicated valve ???
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Going to put a stepper motor to control the bleed valve? ;D Now it gets interesting, as you could control it either with a pot or digitally. More complicated though. Just brainstorming. https://www.electronicshub.org/stepper-motor-control-using-arduino/ (https://www.electronicshub.org/stepper-motor-control-using-arduino/)
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As you decrease the size of the bleed port, you make the valve progressively harder to tune.... and more susceptible to tiny changes in hammer strike.... This is because the valve is mostly "blowing open", the hammer (solenoid) is only initiating the process.... With the bleed port closed (almost) completely, you end up with effectively a spool valve, that will dump the entire reservoir once opened.... Backed just off from that, it will operate like a Cothran valve, with a plateau and cliff.... The only was to change the velocity is with pressure (or by restricting the porting)….
Bob
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Could one restrict the port by using a needle valve? And tune that with some control? Just wondering how to get back to electronic tuning. I think that mechanical tuning is well understood by the crowd here, myself excluded. I'm struggling to learn. Valve types, etc. are not yet part of my vocabulary.
From my training, long, long, ago, it was emphasized there there was an analog between electrical and mechanical systems. So there should be a way to do (something like) this.
Correct me if I'm wrong, the initial exercise was to make an electrically tunable (for FPE?) airgun? Something that one could enter pellet or slug weight and dial in the desired FPE? And electronics would calculate the correct dwell for the valve, and whatever other things needed to be changed? (Assuming the pressure was adequate to actual get that FPE). Or is that just my wish list ;D
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Could one restrict the port by using a needle valve? And tune that with some control? Just wondering how to get back to electronic tuning. I think that mechanical tuning is well understood by the crowd here, myself excluded. I'm struggling to learn. Valve types, etc. are not yet part of my vocabulary.
From my training, long, long, ago, it was emphasized there there was an analog between electrical and mechanical systems. So there should be a way to do (something like) this.
Correct me if I'm wrong, the initial exercise was to make an electrically tunable (for FPE?) airgun? Something that one could enter pellet or slug weight and dial in the desired FPE? And electronics would calculate the correct dwell for the valve, and whatever other things needed to be changed? (Assuming the pressure was adequate to actual get that FPE). Or is that just my wish list ;D
"...electronics would calculate the correct dwell for the valve, and whatever other things needed to be changed..."
Though electronically tune-able to a degree, this design was never going to be "smart". It does not calculate or adjust anything on it's own. You'll need to integrate a computer to do that. I think Daystate does that.
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As you decrease the size of the bleed port, you make the valve progressively harder to tune.... and more susceptible to tiny changes in hammer strike.... This is because the valve is mostly "blowing open", the hammer (solenoid) is only initiating the process.... With the bleed port closed (almost) completely, you end up with effectively a spool valve, that will dump the entire reservoir once opened.... Backed just off from that, it will operate like a Cothran valve, with a plateau and cliff.... The only was to change the velocity is with pressure (or by restricting the porting)….
Bob
That confirms most things I'm seeing. Though I have seemed to stumble on a combination that seems almost impervious to pressure changes. It had a broad plateau. See next...
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I did some tests with the plunger weight installed. FPE was mostly unchanged but it did seem to improve the consistency. I still could not get 80fpe no matter how much I energized the plunger/hammer. I'm limited to about 36v so I could only throw more capacitance in. Maybe higher voltage is needed. I could get 70+ FPE at the higher pressures 2700-3000psi. 60Fpe was easier so I ran a string at that setting. With this Motorhead valve in it's current form, does 60fpe in .22 caliber fairly easily, more than that is pushing it. If I want more fpe, I'll need to tackle the valve. So it's going to be a 60fpe tune for now.
I filled the 226cc plenum (this is a GEN2 tube) to 3000psi and shot a string with the 43g plunger. No regulator, no bottle feed:
43g plunger, 36v, 7500uf
.177, JSB 34g Beast
fps, psi (approx from small gauge)
908, 3000
903
899
899, 2800
901
894, 2700
886
896, 2600
895
886, 2500
901
907
898, 2400
904
886, 2200
895
904
890, 2100
891
883
887, 2000
---------- call it done, as fps falls off after this
880
876
872
862, 1850
first 21 shots, 3000-2000psi
avg fps = 896
SD fps = 7.3
avg FPE = 60.6
The 20+ consistent shots at 60fpe from an unregulated Marauder 226cc tube seems surprisingly good. I calculated that if I had the .45L, 4500psi bottle installed and regulated down to <3000psi, I would get 100 shots at 60fpe.
I tried a few more plunger weight/stroke combinations, but nothing got any better than shown above. I'll use the 43g plunger/brass weight for now. When I get the silicon-iron bar, I'll make a new plunger to try. But, at this point, I'm not expecting much/any improvement from any future plunger/hammer changes.
A 2800psi bottle regulator should arrive tomorrow. Now to decide which is better, 2000psi (actually about 2100psi according to the gauge), or the 2800psi. I will pick based on what pressure seems to give the lowest SD. Based on the shot string, the “plateau” probably starts somewhat above 3000psi and extends down to 2000psi. I'm thinking that the 2800psi set point will be better. I should get about 50 shots on the reg and and then another 30+ good shots off the reg.
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.22, JSB 34g Beast, not .177
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Or ... heavier hammer mass with a very short stroke ???
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Or ... heavier hammer mass with a very short stroke ???
I can't go much heavier (maybe 50g plunger). I prefer the lighter if possible. A little more efficient for lighter pellets.
Assuming I want to tackle the valve:
What about increase the valve lift a little (cut back poppet face about .04" -.05" ), and reduce the bleed hole a little (70% of current area).
Balance chamber would pressurize slower, hammer/plunger would continue a little longer and open the valve another 30%.
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Or ... heavier hammer mass with a very short stroke ???
I can't go much heavier (maybe 50g plunger). I prefer the lighter if possible. A little more efficient for lighter pellets.
Assuming I want to tackle the valve:
What about increase the valve lift a little (cut back poppet face about .04" -.05" ), and reduce the bleed hole a little (70% of current area).
Balance chamber would pressurize slower, hammer/plunger would continue a little longer and open the valve another 30%.
All doable miens ... just not sure the poppet in the valve I provided to you will take .a .050" sealing side trim ? I've done so many styles of these valves I honestly don't remember the specifics of your valves poppet construction ???
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Or ... heavier hammer mass with a very short stroke ???
I can't go much heavier (maybe 50g plunger). I prefer the lighter if possible. A little more efficient for lighter pellets.
Assuming I want to tackle the valve:
What about increase the valve lift a little (cut back poppet face about .04" -.05" ), and reduce the bleed hole a little (70% of current area).
Balance chamber would pressurize slower, hammer/plunger would continue a little longer and open the valve another 30%.
All doable miens ... just not sure the poppet in the valve I provided to you will take .a .050" sealing side trim ? I've done so many styles of these valves I honestly don't remember the specifics of your valves poppet construction ???
I woke up at 5am with the valve on my mind. I wanted to tackle that next and could not wait.
The main modification will be something that slows the pressurization of the balance chamber. I'm not sure I have the fine machining/drilling down well enough to make the hollow stem with smaller bleed vent. The other option is to enlarge the balance chamber. That seems like an easier approach. I figured I need about 30+% to reach 80fpe.
I took the gun apart again and disassembled the balanced valve to see what could be done without risking messing it up.
(http://www.scotthull.us/photos/Armada/IMG_2438.JPG)
What the heck is that little spacer inside the spring in the balance chamber?
It could be a stop, or maybe someone (Motorhead) wanted a smaller balance chamber volume at some point and put the spacer in to take up volume. I calculated that removing the tiny spacer would increase the balance chamber volume by about 14%. That's almost half of what I need. I considered drilling the bottom center of the chamber a little bit deeper in order to gain a little more. Rather than do something I might regret, I decided to just remove the spacer and see what the 14% increase in volume would do.
Reassemble the gun. Lost one of the long skinny breech screws in the process. Decided to run it with three until I can get another. I need to order at least three since I shortened two of them when experimenting with a rear cap configuration that is now obsolete. I need a new rear cap as I've cut/machined the original factory item quite a bit.
First test:
34gr starting at 2800psi
964
962
951
fill again
972
25.39g
1056
1050
Wow - that was easy. For the heavier pellets, I gained about 10fpe by simply removing that tiny spacer. I need to check consistency over a longer shot string. If that checks out, I'll probably be increasing the chamber volume a little more. Maybe cutting the poppet face back 0.04"-0.05". There is enough material. But that could push the bleed port closer/into the valve body/stem-hole. I need to see how much I can really cut it back. It could give me 10% more volume in the balance chamber. And drilling a small pocket at the bottom of the balance chamber will get me a little more. I'm now hopeful that I can get 80fpe.
After going to so much effort on the hammer side and eking out only small additional gains from that, these valves are almost "magical".
Motorhead,
Thanks again for the valve. I'm starting to really appreciate your design and fabrication ability. You mentioned that an adjustable bleed vent would need a design that could be manufactured without too much complexity. Looking at it, a solution for manufacturing is not apparent. So what about a balanced valve with a externally swappable balance plenum?:
(http://www.scotthull.us/photos/Armada/valve-balanced-01.jpg)
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Lol ... that little spacer REDUCES the internal volume of the chamber. At full lift or when spring is at coil bind the spacer fills the space on springs I.D.
Removing it the chamber volume will increase and come up to pressure a tad slower.
Yup your on it !
As to the fabrication skills .. thanx ;)
Currently I have converted my 3 primary rifles using these valves to the INVERTED style. Because the spring is now external you have not only gained more room to change the internal chamber volume in general, but can do so by simply screwing the inner o-ring sealed thimble up/down within the intake grate. How you retain the external spring does not matter & actually NOT having the spring sit on a shoulder at intake grate would allow an even greater range of chamber volume adjustment.
* Second pic while spring sits on a shoulder on the thimble, it with a longer spring could just as easily go all the way up against the intake grate.
Point of this picture is showing that the thimble is threaded into the intake grate and this where you could with a purpose built part get the adjustment range I'm speaking of.
Scott S
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I went to the shop yesterday and proceeded to mess up the valve in the search for knowledge. I got a little higher FPE but inconsistent and it was now leaking. Not the 10fpe increase that I was hoping for. After several disassemble/mod/assemble/test cycles, I went back to the drawing board and studied the valve, and consulted with Motorhead. I have a new plan for some minor valve tweaks. It will be a several days before anything is ready to test.
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Oups .... sometimes seeking knowledge hurts ones progress :P
you'll be back up and running soon enough
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I decided to stay with the non-"inverted" design for the balance chamber, but I did move the spring to the outside of the chamber (along with a few other small changes). The balance cylinder will be a small section of SS tubing pressed into a 3D printed grate. Piston will be 0.25" diameter. Though not needed for function, I'm keeping the removable poppet seat but going to a flat face.
(http://www.scotthull.us/photos/Armada/valve-balanced-04.jpg)
(http://www.scotthull.us/photos/Armada/valve-balanced-02.jpg)
(http://www.scotthull.us/photos/Armada/valve-balanced-03.jpg)
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Tapered seat flow better and does not deform as readily from the closing impact forces.
Good luck my friend ... learn as you go
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Tapered seat flow better and does not deform as readily from the closing impact forces.
Good luck my friend ... learn as you go
I might try to optimize flow later. After I get the functional details right. I could go to a brass or stainless steel seat if deformation of the aluminum is a problem, in which case, the removable seat would be needed.
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I've been doing a more thorough review/redesign of the valve and valve-actuator interface.
The Marauder valves don't have any seal where the stem exits the valve body. That omission saves a little effort/money in manufacturing, and since the dwell is only 1-2 ms, a little leakage is usually inconsequential. A conventional hammer has some expansion areas between it and the valve body, and the hammer is often vented to prevent pressure affects - so no problem. Unfortunately, on my project, the solenoid actuator is in direct contact with the valve body, so nowhere for leakage to escape except into the plunger area. The plunger is 0.438" diameter. The valve stem sees 2000-3000psi. It won't take much leakage to fill any voids in the solenoid, and even 330psi would then be enough to completely override the maximum holding force that the solenoid is generating. I already have the balance chamber trying to close the valve against the hammer/plunger mass, but also the reverse pressure on the plunger itself. That could be the reason that I could never get the dwell to increase much no matter how hard I hit the valve.
My first solution was to vent the interface between the valve body and solenoid. A simpler solution, which might also give me a small efficiency increase, would be to add an o-ring seal to the exit of the valve stem. So that's what I'll do first. It's still going to be several days before I get things back together.
(http://www.scotthull.us/photos/Armada/valve-balanced-05.jpg)
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Great idea and application of a mechanical seal.
would agree than any pressure / volume of air escaping around the primary valve body poppet stem interface is going to counter the electronic driven solenoid being that there is no place for the leaked air to go ?
Great R&D here Scott ... it's definitely all good stuff !!
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Found my post from 4+ years ago on said subject http://www.marauderairrifle.com/forum/viewtopic.php?f=28&t=12022#p79308 (http://www.marauderairrifle.com/forum/viewtopic.php?f=28&t=12022#p79308)
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Found my post from 4+ years ago on said subject http://www.marauderairrifle.com/forum/viewtopic.php?f=28&t=12022#p79308 (http://www.marauderairrifle.com/forum/viewtopic.php?f=28&t=12022#p79308)
Read it all last night. Thanks.
Well - with this new info, I will be modifying the valve, and then I'll need to go back and run much of the tests that I already did. I tabulated a bunch of spreadsheet simulations that I ran today, showing some data that I was interested in:
(http://www.scotthull.us/photos/Armada/pcp-calc-00.jpg)
I ran 2700psi, 2400psi, and 2000psi with various dwell times. I received the 2800psi regulator, but it reads closer to 2700psi so that's the pressure I used. I'm speculating reasons why I see a slight drop in the simulation performance when I increase the dwell past a certain point. It could just be the way I avoided recursion errors by jumping a row, so it might be a row value rounding error. I also noticed that the decrease happens only when pressure in the barrel is kept above the 1500psi range. It could have something to do with the variation in the compress-ability of air in the 1000-3000psi. It varies about 10% from low to high. And trying to move a denser column of air. I'll look into it more later.
The last column on the right shows what dwell it should take to get a 34gr to 80FPE at the three pressures. If I go with 2000psi, the on-reg shot count is highest (83 shots), but it's blowing more residual PSI (430psi) at the muzzle, so it will probably be louder, and not as efficient. At 2700psi, it shows 262 psi at the muzzle, so quieter, but on-reg shot count is only 66 shots. As I saw in earlier tests, for a high starting pressure of 3000, it is possible to get many good shots off-reg. Dwell naturally increases as pressure falls off. So the total shot count might actually be better if the reg is set to a higher pressure, and I can keep the curve flat.
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What is the volume of your plenum, and what are the port sizes and bottle volume and pressure?.... I can run your numbers through Lloyd's spreadsheet....
Bob
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What is the volume of your plenum, and what are the port sizes and bottle volume and pressure?.... I can run your numbers through Lloyd's spreadsheet....
Bob
I just looked, and the plenum size used for those calculations was 215cc. That's for a gen1. Since this is a gen2, I should have used 226cc, I think. But that should not make much difference.
This is all the input data that I used:
caliber: 0.218"
reg pressure: 2000psi, 2400psi, 2700psi
plenum: 215cc
port diameter: 0.168"
pellet mass: 34gr
air temp: 70F
air density: 1.225 kg/m^3
gas constant: 287.058 R J/kg*K
coef: 0.1
bottle volume: 0.45 liter
bottle pressure: 4500psi
barrel length: 28.3"
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I used your numbers in Lloyd's spreadsheet, and in addition 1 lb. of pellet drag and 2 lbs. of breakaway drag, and a transfer port (wasted) volume of 0.02 CI.... I used Isothermal expansion while the valve is open and Adiabatic when closed.... and included the air mass in the calculations (I believe Lloyd's calculator adds 1/2 the air mass released by the valve at each 0.000010 sec. time increment).... In addition, I used 100% efficiency, which as you know never works for Lloyd's calculator.... With a 0.168" transfer port about 70% would be more appropriate....
At 2700 psi, any dwell past 0.0031 sec. resulted in the pellet leaving the muzzle before the valve closed.... The MV was 1317 fps (131 FPE)…. At shorter dwell, I get the following....
0.001 sec.... 900 fps (61 FPE)
0.0015 sec.... 1120 fps (95 FPE)
0.002 sec.... 1242 fps (117 FPE)
At 2400 psi, maximum dwell is 0.0032 sec.... resulting in 1268 fps (121 FPE)…. For shorter dwells....
0.001 sec.... 824 fps (51 FPE)
0.0015 sec.... 1043 fps (82 FPE)
0.002 sec.... 1173 fpe (104 FPE)
At 2000 psi, maximum dwell is 0.0035 sec, giving 1192 fps (107 FPE)…. Shorter dwell gives....
0.001 sec.... 714 fps (39 FPE)
0.0015 sec.... 925 fps (65 FPE)
0.002 sec.... 1063 fps (85 FPE)
Reducing the efficiency to 70% (much more realistic for 0.168" porting) gives the following....
2700 psi, 0.0037 sec, 1100 fps (91 FPE)….
0.001 sec.... 664 fps (33 FPE)
0.0015 sec.... 854 fps (54 FPE)
0.002 sec.... 976 fps (72 FPE)
0.0025 sec.... 1049 fps (83 FPE)
2400 psi, 0.0039 sec, 1058 fps (85 FPE)….
0.001 sec.... 604 fps (28 FPE)
0.0015 sec.... 788 fps (47 FPE)
0.002 sec.... 913 fps (63 FPE)
0.0025 sec.... 992 fps (74 FPE)
2000 psi, 0.0042 sec, 995 fps (95 FPE)….
0.001 sec.... 517 fps (20 FPE)
0.0015 sec.... 689 fps (36 FPE)
0.002 sec.... 815 fps (50 FPE)
0.0025 sec.... 901 fps (61 FPE)
You may be interested in what I achieved with my regulated .22 cal Disco Double (135 cc plenum), running at 2000 psi with a 28" barrel, and full bore-area porting and retractable bolt nose, shooting 34 gr. pellets.... A dump shot gave 997 fps (75 FPE) at 0.43 FPE/CI.... Decreasing the dwell to drop the velocity to 990 fps used half the air (0.88 FPE/CI)…. At 963 fps (70 FPE) that increased to 1.25 FPE/CI.... The final tune was 942 fps (67 FPE) at 1.42 FPE/CI.... My estimate of valve closure is at 32% (9") from the breech (0.002 sec), and I can get Lloyd's calculator to agree with that result by using an efficiency of 85% (typical for bore-sized porting at 2 mSec dwell)…. Calculated muzzle pressure is 406 psi....
Bob
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Bob,
I use a coef (coefficient of friction) of 0.1 where drag force is proportional to caliber and velocity at any point in the barrel. I used 0.5cc (0.03 ci) port volume so we are close to the same there. I use adiabatic expansion through the whole process. Your isothermal model for the valve open phase should still work ok for large plenum volumes. I include the actual air mass (based on adiabatic expansion). Port size (area) is already taken into account in the flow model, so I don't make any "efficiency" adjustments. The 0.168" port has choked flow only after pellet velocity reaches 787fps. If the pellet were to reach 1038fps, then the "efficiency" at that point would be 76% (787/1038). But that is already accounted for in the flow limits of the 0.168" port. The coef is the only thing I fudge to account for "efficiency" losses.
My spreadsheet values seem to fall somewhere between Lloyd's spreadsheet at 70% "efficiency" and 100% efficiency. That makes sense.
The results from your .22 Disco double and .22 Hayabusa shows what's possible. I did get 78fpe early on with the 34gr at 3000psi. I think 80fpe at 2700-2800psi is doable, and still have a decent shot count. I just need to sort out the valve and actuator. I might need to open up the port a little more.
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I did the valve modifications. Here are some specs:
Stem diameter: 0.125"
Maximum stem travel: 0.09" (>=0.04" gives full flow)
Acetal poppit head
Aluminum valve seat (concave conical taper)
Poppit seat diameter: 0.375"
Balance cylinder diameter: 0.25"
Throat diameter: 0.25"
From repeated assembly/disassembly, I pulled one of the wires off the 0.6 ohm solenoid, and it is sealed. I ordered another one, but I have a weaker 0.8 ohm solenoid that I tried tonight. At the voltage I'm running (35v), 0.8 ohm solenoid will never have enough force to hold the valve open, even at 2000psi. But it will still create enough plunger inertia to crack the valve. After assembly, it would not fire no matter how much capacitance I tried. I finally tapped the plunger with a drift and hammer and fired it. After that, it would fire by using the solenoid. With the weak hammer strike, I was only getting about 53fpe at 2000psi. But the valve seems to be working again. No leaks, but still some blow-by, either the transfer-port or valve stem. I did put an oring on the valve stem but I'm not sure how effective it is. I think I'll go ahead and cut some vents so that any leakage is directed away from the plunger. The valve seems to get re-stuck if I leave is sit for a couple hours (stiction)?
The balance/poppit area ratio is only 44%. That does not seem like all that much assistance. Maybe I should reduce the poppit seat diameter some. For 50%-60% ratio? Any feedback from the experts on the poppit seat diameter is appreciated.
I modeled the solenoid and valve stem in a spreadsheet. That was enlightening - i.e. holding voltage requirement vs pressure once the valve is open. For my 35v system, I best stick with 2000psi if I want to control it electronically.
If anyone has any spare Marauder valve bodies (only the body is needed). I could use some more to experiment on.
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I cut some vents in the valve face:
(http://www.scotthull.us/photos/Armada/IMG_2464.JPG)
Since I'm at my desk more than in the metal shop, I'll sometimes 3D print a jig or fixture to make the shop work easier.
Fixture for holding valve body at 45 degrees rotation in a vice:
(http://www.scotthull.us/photos/Armada/IMG_2456.JPG)
I decided to keep trying to get dwell via the solenoid holding force, so the valve has only 0.09" of lift. Balanced valve parts, including 3D printed grate with stainless tube pressed in as the balance chamber.:
(http://www.scotthull.us/photos/Armada/IMG_2461.JPG)
I've been running a 35v system. Today I ordered a 50v boost converter and capacitors. I'll probably need it if running at higher pressure (>2500psi) and higher energy output (>80fpe). More voltage to the solenoid is the equivalent of a hammer spring with more force, without the extra cocking effort.
I cinched down the breech tight and did not notice any blowby in the last test. But that warps the breech with the PEEK transfer port tube resisting crushing enough to slip paper underneath and that makes the shroud touch the end of the air tube.
(http://www.scotthull.us/photos/Armada/IMG_2467.JPG)
I think #10 screw in the middle of the magazine cutout, and anchored to the valve, would be an improvement. Because of the flimsy front-back bridge on the Marauder breeches, I never liked mounting scopes to the rear breech half on a Marauder.
(http://www.scotthull.us/photos/Armada/Armada-breech-00.jpg)
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Scott ... FYI that is exactly what JSAR is doing with the RAPTORS, tho location in there rifles due to a wider MAG slot has the screw radially in line with the 3 holding valve in.
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The new 0.6 ohm solenoid came in the mail this afternoon so I got to try it:
2000psi with 0.4" free stroke and 39gr hammer/plunger, 1 capacitor engaged:
34gr@913fps = 63fpe
3000psi with 0.4" free stroke and 39gr hammer/plunger, 2 capacitors engaged:
34gr@992fps = 74fpe
I only got a couple shots off at the higher setting before fps/fpe fell off and valve finally stuck open blowing out the last of the air at a moderate rate.
(http://www.scotthull.us/photos/Armada/IMG_2468.JPG)
The existing parts might be salvageable if they will press apart. I'll go back to the shop and fix the poppit assembly, maybe rough up the mating surfaces so they have more bite. Or make new parts that thread together? And also put a spacer in the bottom of the balance chamber to act as the stop, so it can't get stuck open if it fails again. And reduce the poppit face diameter (from 0.375" to 0.34") to make it easier to open at higher pressure.
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So what your saying is .... The Acetal SEAT ( outer shell ) stayed against the valves sealing surface and the solenoid strike on stem is driving the inner core out ?
While I have thought about that being a possibility with these shelled type poppets, not had it happen personally ???
Bit more interference fit and some 640/680 loc-tite sleeve retainer compound. ( Or at lease roughen up the surface within the fit and apply a locking agent. )
Tho said .. your learning, tho by way of OLD SCHOOL being that of failure :P
You will get it sorted, that I'm sure of ;D ;D
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So what your saying is .... The Acetal SEAT ( outer shell ) stayed against the valves sealing surface and the solenoid strike on stem is driving the inner core out ?
While I have thought about that being a possibility with these shelled type poppets, not had it happen personally ???
Bit more interference fit and some 640/680 loc-tite sleeve retainer compound. ( Or at lease roughen up the surface within the fit and apply a locking agent. )
Tho said .. your learning, tho by way of OLD SCHOOL being that of failure :P
You will get it sorted, that I'm sure of ;D ;D
That is what happened. I was able to get it pressed apart. I also noticed a flare developing on the poppit perimeter. That could be increasing the diameter and make it harder to open after more use. Like this:
(http://www.scotthull.us/photos/Armada/Armada-poppit-01.jpg)
For now, I roughened the joining surfaces and reglued it with Loctite 648. I tapered the end to 0.32" diameter. That gives about a 61% balance ratio, but that assist will probably drop a little as the poppit flares.
(http://www.scotthull.us/photos/Armada/IMG_2471.JPG)
It got me thinking that the control of the poppit diameter should be the harder aluminum seat, not the Acetal poppit:
I need to let the poppit cure for 24 hours before I test it again. Today, I plan on going to the shop and adding that #10-32 screw to secure the middle of the breech and reduce/eliminate the bowing in the middle.
Later, I'm going to remake the seat with the raised face, and make a poppit that threads to the aluminum balance piston (I will still use Loctite on it).
(http://www.scotthull.us/photos/Armada/Armada-poppit-00.jpg)
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That is the exact reason behind the ANGLED seat on the valve side of the sealing surface. The angle pushes inward on the poppet and the poppet itself has less tendency to flair outward ...
Odd that you did not appear to be having this issue with the valve as first sent to you ? Whats changed ???
As too a raised seat, as your are likely aware .. or not ? The rim of the seat will pound into the softer poppet side and not only flair it, but can fracture it just like near every Gen 2 M-rods does eventually.
** Now if you make the poppets outer shell from PEEK and lapp into the angled seat you get the best of both worlds !!
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That is the exact reason behind the ANGLED seat on the valve side of the sealing surface. The angle pushes inward on the poppet and the poppet itself has less tendency to flair outward ...
Odd that you did not appear to be having this issue with the valve as first sent to you ? Whats changed ???
As too a raised seat, as your are likely aware .. or not ? The rim of the seat will pound into the softer poppet side and not only flair it, but can fracture it just like near every Gen 2 M-rods does eventually.
** Now if you make the poppets outer shell from PEEK and lapp into the angled seat you get the best of both worlds !!
What changed? - no angle and maybe softer material.
I looked at the stock GEN2 valve seat. The raised rim appears to have almost a wedge poppit face. That makes easier sealing but higher stress. I'll try it as I drew it with sufficient contact area (no wedge) to avoid fracture.
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I had already modeled the internal ballistics (barrel) in a spreadsheet (numerical integration). It's close enough that I can use it rather than test all possibilities. When it came to the valving, I was not getting the seat-of-the-pants results that I had expected. So I recently modeled the valve in a spreadsheet (numerical integration). It needs some refinement, but it's seems to be close. The position of the plunger/hammer vs time, and the valve opening vs time can be determined by the spreadsheet. With whatever precision that I want. It has been enlightening enough that I am currently making changes to my system based on spreadsheet simulations. I trust it as much as if I had taken actual position measurements. Position sensing will tell us what happens after we make a physical change. Simulations tell us what will (probably) happen before we make the change. It tells me that I'll have a lot more control with a 50v system. Awaiting part shipments.
Screen shot of solenoid-valve action in spreadsheet, at 50v, 4400uf:
(http://www.scotthull.us/photos/Armada/plunger-valve-timing-00.jpg)
red cells indicate that there is sufficient force to hold the valve open. green field cells indicate when the valve is open. A 0.0000 in the "velocity m/s" column indicates when the valve is held full open. When running at over 2000psi with only 35v, I can slow down the closing a little, but never hold it. 50v will give me more control.
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I got a few things in the mail and have been working on some refinements.
The trigger group uses the Marauder trigger blade, a microswitch, and a 3D printed housing that ties it all together. The action/feel of the trigger is superb:
(http://www.scotthull.us/photos/Armada/IMG_2485.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2486.JPG)
I decided to open op the transfer ports a little more on this go-around. I was not comfortable going straight down with a larger port, as it would come close to breaking into the high pressure side, so I decided to angle the passage away 10 degrees in relation to the thin wall. I 3D printed a fixture/jig to simplify setup and guide the drill:
(http://www.scotthull.us/photos/Armada/Armada-port-angle-00.jpg)
(http://www.scotthull.us/photos/Armada/Armada-port-angle-01.jpg)
(http://www.scotthull.us/photos/Armada/IMG_2484.JPG)
Unless I decide to go with a retractable pellet probe, the maximum beneficial diameter for the porting is about 0.196".
Some 50v capacitors also came in the mail. Still waiting on the 50v boost converter. I have a large military power supply/battery-charger in the shop that is adjustable up to 144 volts DC. While waiting for the small 50v boost converter, I plan on running some tests using the mil-spec supply.
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Free fall down the rabbit hole you go !!
looking forward to seeing leaks stop, stable parts performing reliably as they get beat up on.
Looking good Scott .. keep on plugging along !!
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awesome!!!!!
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Free fall down the rabbit hole you go !!
looking forward to seeing leaks stop, stable parts performing reliably as they get beat up on.
Looking good Scott .. keep on plugging along !!
And that "rabbit hole" is turning out to be a lot deeper than it looked.
The 0.196"porting won't do me much good unless I can continue it to the pellet base. That necessitated some more changes - four 0.098" ports arranged radially in the thimble. And that means sealing to the outside of the thimble. And that means no longer sufficient "meat" to have an internal oring for the probe. Deeper and deeper we go...
(http://www.scotthull.us/photos/Armada/Armada-tport-00.jpg)
(http://www.scotthull.us/photos/Armada/IMG_2490.JPG)
(old thimble in background-right. Thimble on left is a work in progress). I cut an oring groove on the factory probe. Very carefully as not much to work with, and I did not want to mess it up.
I had some correct size xrings handy, so that's what I used. A side benefit of the probe oring is that I won't be blowing the oring out every time I forget to secure the bolt.
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Quad on the probe ... Nice !!
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I got some 50v capacitors but the 55v boost convert still has not arrived. I really wanted to test it at a higher voltage so I drug out an old mil-surplus variable supply. 6-144v variable, but no voltage or current regulation. It was originally used to charge banks of lead acid batteries.
(http://www.scotthull.us/photos/Armada/IMG_2503.JPG)
I bypassed the 35 volt boost converter and hooked the capacitor circuit up to the mil-spec supply. I did not get too much testing in before I melted some solder joints and blew a component. I forgot to check the ratings on the TL783 that I was using as a charge current regulator. I managed to get some shots over the chrony before I let the smoke out of it and it quit working. I had some LM317 regulators that I wanted to try anyway. Though they can't handle 50v either. So I ordered some LM317HV (high voltage) versions that should work when I finally go to 50v. I decided to end the 50v tests until I got the higher voltage components in, but the 50v tests that I did run showed me a couple shots of 34gr@1022fps (78.9fpe).
(http://www.scotthull.us/photos/Armada/IMG_2506.JPG)
That 55v boost converter is coming from China so who knows when. I was impatient so I recently ordered a 48v converter from a stateside source. I did some small refinements while I wait for components.
Radial ported thimble:
(http://www.scotthull.us/photos/Armada/IMG_2497.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2500.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2502.JPG)
Did not notice any performance changes as a result of the new thimble. Thought pellets load a little more smoothly. I worked on some leaks and went with a slightly larger balance chamber, and heavier hammer (43gr). I hope to avoid the valve lock that I was experiencing a few days ago.
With a longish hammer stroke. I get a 52fpe tune that is very stable over 2000-3000psi. Just by shortening the hammer stroke, I get a 65fpe at 3000psi, dropping to 55fpe at 2000psi. The 2800psi regulator on the bottle is not very stable (varies between 2500-2750psi lately). On the long stroke tune, that won't matter. If I can get the regulator to hold a more stable pressure, I should be OK on the short stroke tune. Which is better?
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With my personal guns regulators modified to have very stable output am having really good luck with shorter hammer strokes in the balanced valve rifles.
Personally prefer the faster lock time and lower cyclic vibration of a shorter stroke set up ... Lighter hammer with a heavier spring and SSG devise.
In my .22 high power slugger ... found 2200 psi makes a very stable 54 fpe tune. * Tho as you have found if regulation is not stable neither is velocity with these valves :P
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Is there a mod that helps stabilize regs? Maybe upgrade the orings to slick them up a bit? Restrict flow at reg output?
I have a couple of the cheapo ones and a good ninja one but my experience so far is extremely limited. The overall design appears the same.
Dave
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With my personal guns regulators modified to have very stable output am having really good luck with shorter hammer strokes in the balanced valve rifles.
Personally prefer the faster lock time and lower cyclic vibration of a shorter stroke set up ... Lighter hammer with a heavier spring and SSG devise.
In my .22 high power slugger ... found 2200 psi makes a very stable 54 fpe tune. * Tho as you have found if regulation is not stable neither is velocity with these valves :P
If I'm willing to accept lower FPE, I can set up the balanced valve/solenoid to give fairly constant velocity over a broader pressure range.
For instance, at 3000psi with 34gr, I can get 75fpe with enough hammer momentum/force. But FPE falls off as pressure falls off. If I reduce the hammer momentum/force to give me only 60fpe at 3000psi, I can maintain the same velocity/FPE all the way down to 2000psi. As was the case during this test:
https://www.gatewaytoairguns.org/GTA/index.php?topic=170568.msg155936000#msg155936000 (https://www.gatewaytoairguns.org/GTA/index.php?topic=170568.msg155936000#msg155936000)
It's a 60fpe (max) gun at 2000psi. It's a 75fpe (max) gun at 3000psi. I'm still trying to get the 34gr to 80fpe at 3000psi. I'm still playing with ways to increase flow and dwell as I do not want to exceed 3000 psi. If I'm tuning for max FPE at a given pressure, I will need a stable regulator.
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I've had good luck with Chinese regulators up to about 2000psi. I've been messing with this newer design Chinese 2800psi regulator for the last couple of days. After a little research, and some purchase experiences, it appears that any Chinese bottle regulators ordered with over 2500psi output are this design. It's actually the same as one that is sold as "adjustable", though this one was supposedly pre-set to 2800psi (or thereabouts), and labeled as such. I see no difference between it and the "adjustable" regulator. This one is adjustable for by rotating the bonnet. But not all that adjustable. It won't quite reach 3000psi, and if you try, it will blow the oring out. If you want 3000psi output, it requires a stiffer belleville stack. There are just too many issues with this thing. I wasted many hours and lots of air trying to get this thing to output 2800psi reliably/consistently. Maybe it's possible, but I'm done with it. I decided that for anything over 2000psi, I'm going with proven Ninja designs. Ninja makes two "airgun" regulators. I'm going with a Ninja 4500>3000psi airgun fill station regulator. I have one already, but it's dedicated to a portable fill tank/station (and I can't get the thing unscrewed anyway!). So I have a new one on order specifically for this project. The small size allows me to retain my long bottle with my current bipod attachment point. The Ninja Flex adjustable regulator might be nice but it is significantly longer than the other.
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I have the ninja that you refer to. It has a smaller top piston, which obviously increases the pressure needed to compress the Belleville stack. The bottom diameter of piston was the same as the others. 5/16”
I haven’t tried to get one of my Chinese ones to 3000, although, like you, I have one of the 2800 psi ones waiting when I get home. (I work 2 weeks away, 2 weeks home).
I have a couple of regs off of pb bottles I am going to play with some when I get home. Also have a bag of bellevilles coming and have been studying disk spring calculations. May play with it some next time home as well.
I would have to think that the less interference the orings cause and maybe restricting flow at output to allow longer closing time would be a good starting point to aid stability.
Dave
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I have the ninja that you refer to. It has a smaller top piston, which obviously increases the pressure needed to compress the Belleville stack. The bottom diameter of piston was the same as the others. 5/16”
I haven’t tried to get one of my Chinese ones to 3000, although, like you, I have one of the 2800 psi ones waiting when I get home. (I work 2 weeks away, 2 weeks home).
I have a couple of regs off of pb bottles I am going to play with some when I get home. Also have a bag of bellevilles coming and have been studying disk spring calculations. May play with it some next time home as well.
I would have to think that the less interference the orings cause and maybe restricting flow at output to allow longer closing time would be a good starting point to aid stability.
Dave
I found out that the 3000psi Ninja airgun reg is only available with an 5/8-18UNF bottle thread. My Bottle is a M18x1.5. I would need to order a new bottle for the different thread. So I cancelled that order before it shipped. In that case, I decided to order a shorter M18x1.5 (0.35l vs longer 0.45l) bottle and the Ninja Flex adjustable regulator from Hajimoto. That bottle is available stateside so the wait won't be too long. I lose some air capacity, but the shorter bottle combined with the longer Flex reg will clear my bipod.
There are a few options for setting up a 3000psi output reg on a bottle. The options I considered or tried:
1) $ Standard Chinese <2200psi regulator re-sprung/shimmed to 3000psi, available in M18x1.5 and 5/8-18UNF - medium length. These are not available/designed for 3000psi. I suspect it would work safely with some mods. Decided to not even attempt.
2) $$ Chinese new design reg, "adjustable" up to 3000psi, M18x1.5 only - medium length. I already tried one preset to 2800psi. Not impressed.
3) $$$ Ninja Custom X 3000psi, non-adjustable, 5/8-18UNF only - short length. I have one on a fill station and it seems stable enough. Requires a long pin actuator (only available from Ninja).
4) $$$$ Ninja Flex adjustable up to 3000psi, available in M18x1.5 and 5/8-18UNF - another 3/8" longer than most.
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More testing today with various plunger masses, including some silicon-iron weights. I thought the extra silicon-iron might increase the solenoid efficiency, but no change. No advantage over brass. A recent change to the porting, I enlarged the path from 0.168 to 0.198 diameter. If that were the only change, and port volume had not changed, I should see the same, or higher fps/fpe. In fact, I'm down a couple fpe from the peak that I was able to get prior to the port change. Rather than continuing to enlarge the single thimble port, I had made a thimble with 4 radial ports. That gave me the total area to match the 0.198" port, but it also increased the port volume from about 0.5cc to about 1cc. I went back to my spreadsheet and ran some simulations to confirm. Once over a certain velocity, a larger transfer port area can help fps/fpe. A larger port volume usually hurts fps/fpe. In my case, the spreadsheet simulation does in fact show a slight performance decrease from this recent change (0.198"@1cc port vs 0.168"@0.5cc port), until I get over 100fpe. Below 100fpe, the benefit of the increased port area is overridden by the increased port volume. When I did an earlier simulation, I had input a larger transfer port, but neglected to increase the port volume.
The only benefit I'm realizing from the radial ports, is smoother pellet loading. The valve body is already bored out to 0.198" dia, so no easy going back there. I can almost get back down to the earlier port volume by reducing the transfer port tube diameter, and going back to a single port thimble. That's about 1 or 2fpe that I can pick back up later.
a) Greater area transfer port can help.
b) A larger diameter transfer port results in greater port volume.
c) Greater port volume hurts.
...so every design and performance criteria set will result in a different optimum port diameter.
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I went back to a single 0.142 barrel port. Tapering from a 0.196 port on the valve body.
(http://www.scotthull.us/photos/Armada/Armada-tport-01.jpg)
I got my 50v control box made. In testing, I found that the current valve/hammer configuration works best at about 38v.
(http://www.scotthull.us/photos/Armada/IMG_2524.JPG)
Hammer stroke before stem contact is 0.156”, Valve lift is 0.08”, though it can blow open to 0.09”.
I got the adjustable Ninja regulator in. Shipping was fast but it was missing the adjustment wrench and pin valve. Hajimoto is going to send me the wrench. Ninja is going to send me a pin valve. I decided to use it as is for now – the bottle on/off valve just won't be usable until I install the pin and spring in the regulator. I 3D printed an adjustment wrench and it works great, and it does not scratch the regulator as is common with the metal wrenches. I adjusted the reg to 3000psi. I let is sit overnight and it seems to be good - no leaks and stable pressure.
(http://www.scotthull.us/photos/Armada/IMG_2521.JPG)
(http://www.scotthull.us/photos/Armada/IMG_2525.JPG)
My 450cc bottle can hold 4500psi. Practical fill pressure (especially in the field) will be less than that. I filled the gun to 4000psi in preparation for a full chrony string.
JSB .22 Beast 34gr
4050psi
test shot, 440.7fps (sticky balanced valve)
test shot, 932.5fps
1 ) 946.4fps 4000psi
2 ) 962.9
3 ) 960.5
4 ) 959.0
5 ) 963.7
6 ) 962.3
7 ) 957.7
8 ) 960.8
9 ) 956.0
10) 965.6
11) 966.1
12) 963.0
13) 959.3
14) 967.7
15) 961.5
16) 955.1
17) 965.0
18) 946.2
19) 966.6
20) 954.8
21) 951.7
22) 946.2
23) 953.5
24) 950.6
25) 947.1
26) 944.9
27) 951.1
28) 948.4
29) 947.7
30) 944.8
31) 946.5
32) 941.9
33) 940.8
34) 941.9
35) 938.4
36) 944.5
37) 942.6
38) 950.5
39) 938.2
40) 942.0
41) 953.3 2900psi
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938.0 (off reg)
937.2
Shots 1-41
average = 952.8fps, 68.6fpe
SD = 8.7fps
FPE/cuin = 1.35
When I don't included the first two shots (sticky balance chamber) and last two shots (off reg), the SD (+/- 1%) is barely acceptable. Hopefully it will settle in and get better. The regulator seems to loose a little pressure as bottle pressure drops, but it's fairly stable as these things go. My spreadsheet predicts 46 shots at 71.8fpe. So not too far off what I actually got. My original goal was to have four levels of FPE. I'm right in there at the third level: "60-75fpe with 25-34gr projectiles, 40 shots/fill". I'm not going to get to the forth level (80-100fpe). I almost reached 80fpe with the 34gr. I probably won't need that last level for my intended purposes of long range bench rest. I should get 60 shots if I fill close to 4500psi. And when shooting the 25.39gr, I'll likely cut the fpe some and end up with significantly more shots.
Tomorrow, I'll finally get to do some 100yd testing.
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very cool , looking forward to groups.
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Scott,
Primary reason behind the ES change as pressure drops in primary tank is that of the regulator and SIZE of actual seat it uses. Ninja still has a HIGH RECOVERY rate design and not one of LOW set point drift.
There is always pressure bearing against the seat INSIDE the sealing margin, higher the tanks pressure more is the slight push this area puts on the spool. On the LP side of spool it reacts to set pressure and degree of push back to get seat to seal is more consistent. It is this very slight differential that has the set pressure actually created being a higher set point with more HP and a slight drop in set point as tanks pressure becomes less.
This a VERY EVIDENT in regulators such as HuMa where this seat area is super super small to mitigate this set point drift with varied HP changes.
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I was up at my friends ranch today to do some 100yd bench rest. Weather was nice and winds were fairly light. I brought 3 pellets types (JSB 34 Beast, and JSB 25.39 Monster, and JSB 25.39RD Monster) and one slug type (NSA 27gr .217). I also have some NSA .218 and wished I had brought those too, but I did not.
The 34gr and 25.39gr both did well at 25yds. The 25.39gr did OK at 50yds, but the 34gr was opening up. By 100yds, the 34gr was not able to stay on paper for most shots. The 25.39gr was not much better. After the dismal 100yd groups with the JSB 34gr and 25.39gr pellets, I did not even bother with the 25.39grRD. I switched to the NSA slugs and they did much better at the far targets, with a decent group at 100yds. This gun has a slug liner after all, so I was then thinking that I would need a pellet liner if I want to shoot pellets at EBR. Just before leaving, I decided to test the JSB 25.39grRD at 100yds. The groups were on par with the NSA slugs. That made my day.
The NSA 27gr and JSB 25.39grRD were shot at 1030fps and 1055fps average. Accuracy was good, but I'm hoping that there is even better accuracy to be had at a slightly reduced velocity. I plan on scheduling another day where I will try some lower pressure and velocity settings, with the NSA .218 and JSB RD Monsters. For pellets, it's now looking like I'll use the JSB (or FX) 25.39gr RD pellets. For slugs in this weight class, there are lots of options out there to play with.
(http://www.scotthull.us/photos/Armada/IMG_2529.JPG)
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some impressive shooting , most of the 25grains could be covered by the quarter !
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I originally was running a 35v system and could open the stock valve at 1500psi, but not 3000psi. With the balanced valve, I could open it at 3000psi. I now have a 50v system so I decided to reinstall the standard Armada valve and see what happens.
3000psi, 34gr, 50v, Armada valve
4700uf - 630fps (30fpe)
9400uf - 770fps (45fpe)
14100uf - 880fpe (58fpe)
18800uf - 914fps (63fpe)
3000psi, 25.39gr, 50v, Armada valve
14100uf - 1002fps (57fpe)
I'm leaning toward a standard valve at this point. It does take a lot of capacitor energy to extend the dwell, but at 50v, it's behaving more like I originally wanted.
I've found out what I can do to improve flow on the Armada factory valve, but I probably don't even need to do that, as it's already giving me close to the desired velocity. I think 50v will work for me with the standard valve. A future upgrade will be a 60v system (awaiting some parts from China).
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very interesting.. are you saying the standard valve is more consitent shot to shot ES ?
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very interesting.. are you saying the standard valve is more consitent shot to shot ES ?
I'm not saying that yet as I have not tested consistency.
The balanced valve is easy to open and dwell can be a function of balance chamber volume and vent size. So no need to use a heavy impact hammer with high mass.
The electronic valve can use voltage and capacitance to open and dwell a valve.
A high power balanced valve has a predetermined dwell bui!t in. So it's not possible to reduce it significantly. FPE is mostly a function of psi as dwell is not externally adjustable to any significant amount. That was fighting what I was trying to do.
The standard valve is harder to open and has no built in dwell. The solenoid can provide acceleration to create hammer energy (crack the standard valve) and a holding force (dwell). Assuming enough voltage (cracking valve) and enough capacitance (dwell), I should be able to have a wide range of fpe at any psi setting. It works with a standard valve, but can't control fpe in a balanced valve.
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very interesting.. are you saying the standard valve is more consitent shot to shot ES ?
I'm not saying that yet as I have not tested consistency.
The balanced valve is easy to open and dwell can be a function of balance chamber volume and vent size. So no need to use a heavy impact hammer with high mass.
The electronic valve can use voltage and capacitance to open and dwell a valve.
A high power balanced valve has a predetermined dwell bui!t in. So it's not possible to reduce it significantly. FPE is mostly a function of psi as dwell is not externally adjustable to any significant amount. That was fighting what I was trying to do.
The standard valve is harder to open and has no built in dwell. The solenoid can provide acceleration to create hammer energy (crack the standard valve) and a holding force (dwell). Assuming enough voltage (cracking valve) and enough capacitance (dwell), I should be able to have a wide range of fpe at any psi setting. It works with a standard valve, but can't control fpe in a balanced valve.
If you're not able to tune within a specific range of fps using a balanced valve that simply means (to me) that either the balance ratios are off (overly balanced leaving too little force to close valve in reasonable time), vent size to chamber volume (resulting in too slow of fill times to act as a conventional valve for closure).
FWIW A balanced valve should be designed for a specific power level / dwell range AND pressure, its not a one size fits all. If you go from a valve lock condition to full open condition, something isn't right in the valves design to allow one to manipulate fps via hammer strike.
A tune-able balanced valve is not easy to make 'perfect'...it takes timing of the chamber being filled down to under 1 ms...trying to achieve that ain't easy...I have a spreadsheet that does this but don't plan to make that public for personal reasons (don't want certain people profiting off of a design the spreadsheet makes for example)
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We had a three man bench rest match today. I shot my .22 Armada. Vince and John shot their .25 FX Crowns. It was to be a pellet match so i shot 25.39grRD which shot well during the last outing when they were at 1055fps. They were now at 980fps and I was hoping for even better. But they were a lot worse. Finished way behind Vince and John. Almost half the shots were completely off the paper. I'll probably try them at about 910-920fps next outing.
After the match, I tried the NSA 27gr .217 slugs. They shot well at 1020fps and were still good at 945fps. I also tried the NSA .218 slugs for comparison. I think they might be even better as the first and only group that I shot with them was a 6 shot sub MOA group at 100 yards.
With the stock valve presently using 3x capacitors to get needed dwell (compared to the balanced valve), I ran the 500mah battery dead after about 100shots.
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...
If you're not able to tune within a specific range of fps using a balanced valve that simply means (to me) that either the balance ratios are off (overly balanced leaving too little force to close valve in reasonable time), vent size to chamber volume (resulting in too slow of fill times to act as a conventional valve for closure).
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That's where I'm at with my balanced valve experiments - not quite right yet. I have not given up on the balanced valve as I see the benefits of a valve that is at least partially self energizing.
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The first electronic hammer that I did was a 12fpe pistol with a 25v system. It worked OK. For this HP Armada, I started at 25v, then 35v, now 50v. Each step worked a little better and required significantly less capacitance as voltage increased. My 50v electronic hammer is showing some promise. With sufficient voltage and a conventional valve, the electronic hammer is giving me considerable control over dwell and resulting fpe. The next step is going to be 60-63volts. I'm starting to see why Daystate uses a 63v system and then over-volts it to 70+volts. Higher voltage takes care of a lot of issues with an electronic hammer.
At this point, I can get 55fpe with a stock Armada valve, or back off on the hammer energy and have it shoot like an unmodified 32fpe Armada/Marauder. I'm hoping that the 63v system will give me a 32fpe-64fpe range without needing to adjust any mechanical components. It would be done electronically.
During this process, there are lots of things that I have wanted to test, and there are even more yet. I've done a lot of back-stepping when something was not right, only to revisit it after gaining a little more knowledge.
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I'm currently working on and testing some options with the circuitry. I'm going to eliminate the voltage regulator as the XL6009 booster seems to have some overcurrent protection in the circuitry. Capacitors will charge a lot faster now. I'm still going to use the RC constant of the circuitry to get a maximum dwell time, but I need to add a timing feature to insure that the caps drain enough to allow the SCR to reset (set the minimum on time). Current needs to drop below 40ma for good assurance. Rather than using the trigger switch directly, it will not activate a fet or relay with an extended on time.
I just ordered a custom solenoid from Solenoid City (Magnetic Sensor Systems). I had been using their 0.9" diameter solenoid as it was listed as available in 22awg wire giving the most force/volt. The 1" diameter solenoids are more efficient and will fit but the listed 23awg wire would require more voltage than I wanted to use. After talking to the tech/engineer at MSS, I was told that I could custom order in other awg sizes. So I have a 1" 21awg solenoid coming that will give me 35% more force at the same voltage while drawing 15% less current. Combined with a 63v system, I should have much better control over the valve opening/dwell.
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thats awesome they will do custom work.. How is it more efficient , is it less resistance, more surface area on the armature? im just guessing
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thats awesome they will do custom work.. How is it more efficient , is it less resistance, more surface area on the armature? im just guessing
More amp-turns makes a stronger magnetic field. So more turns of wire and/or more amps (less resistance) are desirable. More turns means more resistance, unless you increase the wire diameter, but that means room for fewer turns. Larger solenoid OD allows more turns of larger wire. Even though my resistance increased some, I got a lot more turns, so I get more force even with less current flowing. More volume of wire means more turns for any given resistance. This solenoid will be about 50% more efficient overall.
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The first electronic hammer that I did was a 12fpe pistol with a 25v system. It worked OK. For this HP Armada, I started at 25v, then 35v, now 50v. Each step worked a little better and required significantly less capacitance as voltage increased. My 50v electronic hammer is showing some promise. With sufficient voltage and a conventional valve, the electronic hammer is giving me considerable control over dwell and resulting fpe. The next step is going to be 60-63volts. I'm starting to see why Daystate uses a 63v system and then over-volts it to 70+volts. Higher voltage takes care of a lot of issues with an electronic hammer.
This makes sense. The energy stored in a capacitor is given by E = 1/2 c V2 From an energy perspective, it is far better to increase the voltage than the capacitance. Relative energy of a 25V, 35V, 50V, 63V, 70V system (for the same capacitance) is: 1, 1.96, 4, 6.35, 7.84. Of course, higher voltage caps are usually physically larger.
You have been doing some awesome stuff! Following along...
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Some realizations:
For an electronically tuned valve, I don't want a "balanced valve".
The electronic valve uses voltage to provide a solenoid force to open the valve, and capacitance to provide for duration of that force.
The balanced valve uses chamber diameter to provide a force to open the valve, and chamber volume to provide for a duration of that force.
Trying to use both puts them at odds with each other. Early on I demonstrated good electronic control of a standard valve from 12-34fpe. I wanted more FPE, and the balanced valve was an easy path to that end, but it took away most of the control from the electronics. Now that I've moved to more powerful electronics, I'm not going to use the balanced valve.
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Some realizations:
For an electronically tuned valve, I don't want a "balanced valve".
The electronic valve uses voltage to provide a solenoid force to open the valve, and capacitance to provide for duration of that force.
The balanced valve uses chamber diameter to provide a force to open the valve, and chamber volume to provide for a duration of that force.
Trying to use both puts them at odds with each other. Early on I demonstrated good electronic control of a standard valve from 12-34fpe. I wanted more FPE, and the balanced valve was an easy path to that end, but it took away most of the control from the electronics. Now that I've moved to more powerful electronics, I'm not going to use the balanced valve.
Lol ... Next chapter ... Cobra chamber in a conventional valve 8)
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Some realizations:
For an electronically tuned valve, I don't want a "balanced valve".
The electronic valve uses voltage to provide a solenoid force to open the valve, and capacitance to provide for duration of that force.
The balanced valve uses chamber diameter to provide a force to open the valve, and chamber volume to provide for a duration of that force.
Trying to use both puts them at odds with each other. Early on I demonstrated good electronic control of a standard valve from 12-34fpe. I wanted more FPE, and the balanced valve was an easy path to that end, but it took away most of the control from the electronics. Now that I've moved to more powerful electronics, I'm not going to use the balanced valve.
Lol ... Next chapter ... Cobra chamber in a conventional valve 8)
I just climbed out of the last rabbit hole you sent me down. :P
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An Elmer Fudd hat and your all set for Wabbit huntin ;D
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I got the 1" OD, 21awg solenoid in and tested. It is indeed more efficient. I think I'll now be able to use 2200uf capacitors instead of the 4700uf. The 2200uf caps are already working OK and should be even better when I go from a 50v to 60v system. That combined with the higher charging current directly from the booster board, allows the caps to recharge almost instantly after firing a shot. The circuit and EM packaging has been an iterative process. It's taking shape. I have more confidence now that it will do most everything that I originally outlined.
I'm trying to keep the circuit simple/elegant, but some complexity has crept in. I separated the main control from the optional capacitor bank circuit. The main control is always used and I wanted that to be accessible without moving the trigger hand. The extra capacitor bank is now in a separate box. Each capacitor now has a small diode (D1) to isolate charging from the other capacitors. And each extra cap has a larger diode (D2) as a one-way discharge path.
The charging circuit is disengaged while the trigger is being pulled, but if I do a snap pull and release, the charging circuit can reengage before the SCR turns off. And then the SCR won't turn off and the charge current passes through the SCR into the solenoid instead of the caps. If I hold the trigger long enough, it is not a problem. I decided to add a relay that keeps the capacitor charging circuit disengaged for several milliseconds after the trigger is released. So a snap trigger pull/release will no longer be a problem.
The isolation diodes allow me to switch in and out additional capacitance via the three forward rocker switches, even when the system is powered on. However, when switching a booster cap off (or when fine tuning the system voltage), I need to dry fire it once in order to reset that cap back to zero volts. Similar to when you reduce the pressure on an adjustable regulator and you need to dry fire to drain the plenum down to the new set pressure. I thought about putting in a power resistor to quickly bleed down any caps that were switched off, but decided that it was not worth the complexity.
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That is some awesome development! Just browsed through the entire thread.
Slightly disappointed on the fact you reverted back to traditional valve, as the air assisted can be tuned for dwell when you make the chamber port large enough.
But, never mind my disappointment as this is your thread. You are doing some awesome work on the electronics and controlling the valve.
Springless and hammerless systems are the way of the future and harmonic stability of the bigger bore guns.
Marko
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The original
That is some awesome development! Just browsed through the entire thread.
Slightly disappointed on the fact you reverted back to traditional valve, as the air assisted can be tuned for dwell when you make the chamber port large enough.
But, never mind my disappointment as this is your thread. You are doing some awesome work on the electronics and controlling the valve.
Springless and hammerless systems are the way of the future and harmonic stability of the bigger bore guns.
Marko
My original intent did not include a balanced valve, but upon receiving one, I decided to try it. I was impressed with the easy FPE gains with fairly low hammer strikes. My electronic actuator now has enough energy to actuate a conventional valve, even at 3000psi. The conventional valve responds better to varying hammer strikes. The electronic actuator removes all hammer cocking effort. The main advantage of the balanced valve is easy cocking at high FPE. So there was no longer any benefit to me. And the balanced valve contains a dynamic o-ring seal, which means one more seal to monitor, and more stiction than a conventional valve. Minuses outweighed the pluses when using a balanced valve in this application.
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For me the balanced valve is the only option, as all of my valves are with 10mm port or larger. Thats why I was curious how you get it working and was little disappointed.
Nothing to do with your awesome project.
Did you try the smaller solenoid on high voltage, around 80-90v?
Would be interesting to know where the limit is for voltage, before the coil starts to make more heat than actual force.
Marko
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For me the balanced valve is the only option, as all of my valves are with 10mm port or larger. Thats why I was curious how you get it working and was little disappointed.
Nothing to do with your awesome project.
Did you try the smaller solenoid on high voltage, around 80-90v?
Would be interesting to know where the limit is for voltage, before the coil starts to make more heat than actual force.
Marko
The larger solenoid is more efficient but it has the same core as the smaller. If enough voltage/current is applied to either, the maximum force will be the same for either once they saturate, at which point, more voltage/current will be of little benefit. At least that is how I understand it. The larger solenoid has a higher duty cycle for the same force, so it uses less battery energy and runs cooler.
10mm porting indicates a much higher fpe than I am going for. So the balanced valve might then be required to keep the electronics compact enough.
I'm thinking for <20fpe, no balanced valve, no electronics. For up to 100fpe, balanced valve or electronic actuator. For higher fpe, balanced valve or both balanced valve and electronic actuator.
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Well most of my builds are on the larger end of the caliber spectrum. So I need big valves and good amount of balancer force.
Need to see what solenoids are readily available here and see where it goes from that.
Marko
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I have not reported in a couple of weeks, but I have been doing some experimenting. And I'm getting closer to what I want. I've now got the 60v system built and installed.
The current setup has a standard/ported valve (not the balanced valve). I learned some things in the process. When playing with the porting on a standard Marauder valve, I found that increasing the port (and throat) size gives quickly diminishing returns rather than what you might expect. So that alone never got me back up to the 70+fpe that I was getting with the balanced valve. I now have a fast acting solenoid hammer with plenty of dwell, so it should produce more than the low 60's fpe that I was getting. I looked into some other high power .22 airguns, mostly rsterne's Hayabusa. How was that able to make 100fpe AND 1000+fps? Something's different about the Haybusa valve. There was no valve body per se. The valve face/seat was inside the air-tube/plenum. I'd also talked to Motorhead recently about the affects of enlarging the throat and he had mentioned something else about the "impulse". I thought about that some and started to form a theory that it was not the flow rate that was the problem with my valve. The limiting factor might be due to an inadequate impulse. The impulse pressurizes the "lost volume" and starts the pellet on it's way. If the impulse builds too slowly, the projectile travels too far down the barrel before taking advantage of the peak pressure. Getting the high pressure air molecules behind the pellet as soon as possible could be the key. Not only does the valve need to open fast, it needs a readily available supply of air molecules. If the bulk of the plenum volume is too far away from the valve seat, it has trouble assisting the impulse build up. The Haybusa has the full diameter of the plenum right at the valve seat. The balanced valve body that I had been using had been bored out some internally, so there was a little bit more volume there. I re-built the balanced valve body without the balance chamber. The first test with it showed an improvement over the ported Marauder valve. Promising but not conclusive. I took the valve and gauge block into the shop and bored both out significantly while still retaining plenty of material to be safe. The bulk of the plenum was still where is was, but I had opened up about 3cc of volume inside the valve body and about 5cc in the the gauge block/valve interface. I reassembled and tested it. I got about a 100fps increase for all pellet types. FPE went from mid 60's to mid 70's.
The 4 switchable capacitors that I'm currently using are all 2200uf. Settings 0, +1, +2, +3 are 2200uf, 4400uf, 6600uf, and 8800uf. I could swap one or more of the 2200uf for 3300uf if I decide to use heavier projectiles. At 3000psi, the maximum switch setting (+3) is a little hot (1100+fps) for 25.39gr pellets, but the +2 setting gives me 1060fps. That was my target goal for that pellet. The +3 setting is good for heavier 34gr pellets giving about 1000fps. 40gr cast slugs were at 930fps, but I would likely get 950-960fps (80+fpe) by increasing the capacitance for more dwell.
On Monday, I hope to shoot a 100yd benchrest card, probably using the 25.39gr RD Monsters at 1060fps. I also want to test out the JSB 18.13gr and H&N 27gr slugs.
I'm close on all my goals for tune-ability and fpe, except I'm still at the low end of the 80-100fpe HP goal. It will require additional valve volume to get there. Not easily doable with the Marauder type arrangement. I'm actually satisfied with my current max fpe as it is sufficient for the heaviest pellets (25.39gr and 34gr) as well as all slugs (20gr-30gr) from the major manufactures and all but the heaviest new slugs (36gr+) from some of the newer companies.
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AMPLITUDE is in my writing / teaching, is that of how quickly the transfer of energy ( compressed air ) gets in behind the projectile.
Faster you can ramp up this "Impulse" before the projectile starts moving greater will be the reactive forces applied to it.
Very similar to a champagne cork ... The pressure within the bottle is a fixed entity, if cork is slippery / loose fitting it will ease out of the bottle and just lightly Bloop out.
Now if the cork fit is tight holding back the pressure not moving and then made to move a tad it will break free and exit the bottle with much violence !
* A PCP while not a cork in a bottle per-say, does deliver the pressure starting from zero and as the pellet sits there pressure behind it builds until it no longer can resist and starts moving. THIS IS THE POINT .... Amplitude !! By getting the pressure to get closer to operating pressure before motion occurs will deliver the greatest energy transfer of the expanding air against the projectile.
There is much more to this that we won't get into here ... but lets say like the cork in the bottle analogy, if the corks too tight it's not going anywhere !!
many cause & effects of drag mass etc that are amplified at our very low pressures relative to a Powder / Firearm.
Great work Scott H .. You took a tour of the inner workings of PCP valves and came out the other side more educated and enlightened 8) 8)
Good stuff my friend ;)
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thanks for sharing the info.
I have noticed something similar while testing plenum sizes and it’s orientation. I.e having the same plenum mounted linear and on the Z axis with the valve made more power compared to the same plenum mounted on the Y axis. Enlarging it would be my next step.
Looks like I can copy some of your methods and apply them to my projects.
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I’m glad it is going your way. The 60v system seems to be working great. Hope your shoot goes well. This has been a very informative project for me. Thanks again for sharing it.
Dave
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thanks for sharing the info.
I have noticed something similar while testing plenum sizes and it’s orientation. I.e having the same plenum mounted linear and on the Z axis with the valve made more power compared to the same plenum mounted on the Y axis. Enlarging it would be my next step.
Looks like I can copy some of your methods and apply them to my projects.
If you want to maximize the impulse amplitude, then here is some more info. More plenum volume always has some benefit but with diminishing returns. Keeping the path straight is also important but secondary. The top section view in the following image shows what I have currently. Area "A" is the best location to maximize plenum space, then "B", then "C" and so on. The Marauder valve configuration is a limitation in this respect. I did what I could without too much risk. The middle view shows about the max that I could safely do by additional machining of the current valve body. That would likely net me some more fpe at the high end. The bottom view show a section of what an idealized valve body would look like while still fitting a stock Marauder/Armada. A friend of mine has been experimenting with investment casting of 3D models with some success. I might talk to him about the possibility of doing that for this valve.
BTW: The two breech screw holes are shown rotated 90 degrees in order to more easily show their location in the valve body.
(http://www.scotthull.us/photos/Armada/valve-marauder-section-01.jpg)
I did some efficiency testing and it is better than I originally planned for. I should be able to get about 60 shots at 75fpe with a 4500psi fill.
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I just milled an oval slot between the two valve screws (with a 1/2" mill, IIRC), and then turned the valve ID to the same diameter as the height of the hole, front and back....
(https://hosting.photobucket.com/albums/oo221/rsterne/BRod%20Project/.highres/Milled%20Out%20Cobra%20Valve_zpseks73xb5.jpg) (https://app.photobucket.com/u/rsterne/a/0a8cc990-1df6-4f18-aa0b-1ed96c028474/p/8836109d-2a9d-4052-9fb2-6e5ffc8720a5)
I didn't spend a lot of time rounding off the corners of the "pillars" that remained, but I did smooth them with a Dremel after this pic was taken....
Bob
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When you said "increasing" the valve throat and ports, there is some diminishing returns. i wish to hear what you found.
I heard briefly Bob said something about keeping the throat 10% larger than the exhaust to keep the pressure up during shot cycle.
so i am curious about going larger than 10%.
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My recommendation was to have the "equivalent" throat area (throat area minus valve stem) be the equivalent of a hole about 10% over the port size, to avoid any losses from flow around the stem.... The larger you go with the throat, and hence the poppet seat, the more force it takes to open the poppet.... There is a small loss in pressure from having the porting larger than necessary, once you go past full bore area.... but in reality you can go much larger without loosing any noticable performance.... Marco uses a valve with a 9mm transfer port on a .223 cal with great results, and I have a valve built for a .357 in a gun I have used down to .224 cal, with the taper occurring in the transfer port only.... It might be possible to increase the efficiency by using smaller ports, but I'm getting good efficiency now, so why argue with success.... HOWEVER, both Marco and I are using balanced valves, so the opening force, and hammer strike required, is not an issue....
Bob
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I am confused as to how the interior volume of the valve (short of the increase of overall plenum volume) contributed to a 100 fps gain. Not saying it didn't happen, but if it happened for the reason described alone for you, than it should equally or nearly so for me...
I run a very large ported mrod valve at .225" that has its interior otherwise untouched (from valve seat to spring seat)...
You're telling me, I should expect a large increase in fps/fpe if I were to simply bore that area out? Even with me currently making 64 fpe at 2000 psi and 80 fpe at 3000 psi shooting 34 gr?
If that is so, what the heckers am I waiting for? :o
Fwiw my other valve that is ported to .22", and bored out on its interior like you recently done, performed worse than its .225" brother as expected...and that .005" is not worth much more than 10 fps...
Have you considered, the flow around your poppet head due to its diameter and the inner valve diameter? (I run .276"~ poppets so there is much less restriction around the poppet head in a stock valve compared to the .34" OEM poppet OD...)
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Either way, even if the ID of the valve is only 1/2", with a 0.34" poppet OD, that will not restrict the flow more than the throat or ports.... The reason I milled out a slot inside my valve was because it was a balanced valve with a fairly large balance chamber thimble (7/16"? ) that drastically decreased the room for flow through the middle of the valve.... I was starting from a Cobra valve that already had the rear of the valve bored out near the poppet.... so I just made the height of the slot match that diameter....
Bob
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Either way, even if the ID of the valve is only 1/2", with a 0.34" poppet OD, that will not restrict the flow more than the throat or ports.... The reason I milled out a slot inside my valve was because it was a balanced valve with a fairly large balance chamber thimble that drastically decreased the room for flow through the middle of the valve.... Boring out the inside rear of the valve was mostly done so ease the flow from that slot to the poppet....
Bob
No, no. I am referring to Scotchmo's valve. If it was gen 1 marauder .25 cal, it was likely .38" on the interior, and with a .34" poppet, that only allows sufficient flow to support porting of around .17" forward of it...which would explain his lack luster performance prior to remedying this...
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Either way, even if the ID of the valve is only 1/2", with a 0.34" poppet OD, that will not restrict the flow more than the throat or ports.... The reason I milled out a slot inside my valve was because it was a balanced valve with a fairly large balance chamber thimble that drastically decreased the room for flow through the middle of the valve.... Boring out the inside rear of the valve was mostly done so ease the flow from that slot to the poppet....
Bob
No, no. I am referring to Scotchmo's valve. If it was gen 1 marauder .25 cal, it was likely .38" on the interior, and with a .34" poppet, that only allows sufficient flow to support porting of around .17" forward of it...which would explain his lack luster performance prior to remedying this...
IT WAS NOT ... it came from me as a Bone stock gen 2 valve. Scott H bored the I.D to @ .490" down to the @ seat as a mod prior too the time of his post on the I.D area subject.
FYI ...
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Either way, even if the ID of the valve is only 1/2", with a 0.34" poppet OD, that will not restrict the flow more than the throat or ports.... The reason I milled out a slot inside my valve was because it was a balanced valve with a fairly large balance chamber thimble that drastically decreased the room for flow through the middle of the valve.... Boring out the inside rear of the valve was mostly done so ease the flow from that slot to the poppet....
Bob
No, no. I am referring to Scotchmo's valve. If it was gen 1 marauder .25 cal, it was likely .38" on the interior, and with a .34" poppet, that only allows sufficient flow to support porting of around .17" forward of it...which would explain his lack luster performance prior to remedying this...
IT WAS NOT ... it came from me as a Bone stock gen 2 valve. Scott H bored the I.D to @ .490" down to the @ seat as a mod prior too the time of his post on the I.D area subject.
FYI ...
Ahh. So if flow was not an issue. Is there near 100 fps to be had solely from boring the id of an m-rod valve near the seat beyond the gen 2 .42"?
Or better yet, are we certain that boring the ID of the valve near the seat at all, contributes a significant 'pressure impulse increase'?
I don't ask to be pessimistic, I ask because my experience suggests otherwise, and I would degas my rifle and bore it out in a heartbeat if I was told there is definitely significant gain to be had. Thanks.
-Matt
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I don't know ???
Having good luck in owning several WAR bodies that are already modified as such along with several JSAR bodies at @ .520" never searched for more power in such areas or done the tests Scott H is doing. He very well may shed some light on extreme power from smallish valves and enlighten us all :o
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Either way, even if the ID of the valve is only 1/2", with a 0.34" poppet OD, that will not restrict the flow more than the throat or ports.... The reason I milled out a slot inside my valve was because it was a balanced valve with a fairly large balance chamber thimble that drastically decreased the room for flow through the middle of the valve.... Boring out the inside rear of the valve was mostly done so ease the flow from that slot to the poppet....
Bob
No, no. I am referring to Scotchmo's valve. If it was gen 1 marauder .25 cal, it was likely .38" on the interior, and with a .34" poppet, that only allows sufficient flow to support porting of around .17" forward of it...which would explain his lack luster performance prior to remedying this...
Gen 2 valve, when I bored out the throat to 0.25" diameter, there was only a minor improvement (5-10fps). The 0.25" throat with the 0.125" stem gives 0.037"^2 area. The Gen 2 valve has a 0.34" diameter poppet and a 0.42" bore around the poppet. That gives an area that is 0.048"^2. So it is not a flow restriction.
However, enlarging the bore around the poppet will do exactly what I want. It will put more air molecules (volume) right at the valve seat. Those air molecules only need to travel a very short distance to fill the lost volume, with the throat being the only restriction. If they had to travel down a flow path, the maximum bulk velocity that they can reach is sonic. So we are talking about maybe 1/10 or 1/5 of a millisecond slower to aid the impulse pressure. The pellet might end up another 1/4-1/2" down the barrel before reaching the impulse peak.
To confirm my suspicions, I had installed a valve body that had been bored to about 0.5" and got about 30-40fps increase. I did not dare bore larger from the back as the breach screws are close to the 0.5" bore. So I used a boring bar to reach in and bored out a 0.6" long cylinder of 0.625" diameter, right in front of the valve seat. I also bored out the rear of the valve body and the gauge block. All in an attempt to move more of the plenum volume closer to the valve seat. That gave me an additional 60fps. I was now 100fps faster than when I had the 0.42" bore. I'm not saying that it will always work, as it will depend on where your limitations/restrictions are in a particular system. Based on what I experienced, enlarging the volume near the valve seat will be my only path that I will take for additional fpe, at least until that particular change starts to yield diminishing returns.
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Missed the "I also bored out the rear of the valve body and the gauge block"
Ah, there is some restriction in distance right there ! The hole passing threw the gauge manifold / block will indeed slow the transfer of air into the valve and very well may be the reason for a large portion of the jump in power ... Wag here so just bear with me on the idea ???
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I have bored out many valves, and unless there is virtually no plenum volume, I have never seen more than a few fps gain in velocity from increasing the volume inside the valve near the valve seat.... providing there is sufficient clearance between the valve ID and the poppet so that the flow is more than that possible through the throat and ports....
The pressure rise at the pellet is nearly instantaneous, as the pellet is not moving when the valve first opens, and the molecules can fill that space at 1650 fps.... There is no significant "flow velocity" to deal with, as the air can't flow faster than the pellet, once the pressure is nearly equalized, so choking or any form of sonic limiting does not occur.... If the distance from seat to pellet is 1", it only takes about 0.1 mSec. for the pressure at the base of the pellet to reach nearly the pressure inside the valve....
Bob
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Missed the "I also bored out the rear of the valve body and the gauge block"
Ah, there is some restriction in distance right there ! The hole passing threw the gauge manifold / block will indeed slow the transfer of air into the valve and very well may be the reason for a large portion of the jump in power ... Wag here so just bear with me on the idea ???
I meant "I also bored out the rear front of the valve body and the gauge block"
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...the molecules can fill that space at 1650 fps.... There is no significant "flow velocity" to deal with, as the air can't flow faster than the pellet, once the pressure is nearly equalized, so choking or any form of sonic limiting does not occur.... If the distance from seat to pellet is 1", it only takes about 0.1 mSec. for the pressure at the base of the pellet to reach nearly the pressure inside the valve....
Bob
Theorhetically, some molecules can reach a forward velocity of approx 2x the SOS, as the gas is expanding, but the bulk fill velocity is sonic at maximum/at best. I know we are talking about 1/10's of msecs difference. But, if the bulk of the volume needed to fill the low pressure side needs to travel only 1/2 as far, I could see it making a difference. At this point it's all conjecture.
I'm going to move more plenum volume close to the valve seat at some point. If fpe increases more we might be on to something. If not, it's inconclusive at best since the design may have reached some other limiting factor at that point.
This is all with an electronic hammer, so a spring powered hammer might be different. I've got a 40gram hammer contacting the stem at 7m/s. Besides the hammer mass, there is a continual, though tapering (tapering up with travel, and tapering down with time) force held on the hammer. In addition to the momentum used to crack the valve, that tapering force is almost 50lbs at stem contact, building as the valve opens and then falling as the capacitors drain.
I've now got a reliable conventional valve. No cocking effort, except to load the pellet. And 75fpe. I'm liking it.
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Me thinks gaspiston cocking and magazine ;D
Marko
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I think my suspicions are cleared up now, thanks guys...
There is absolutely no way I will gain anything significant (in my configuration, 53 cc volume) by boring the valve near the seat larger than it currently is (.42" to .5"+ some around the screws would net 2-3 cc). According to my calculations I will net roughly 2 fps gain from that increase in plenum volume alone. Is it possible I may gain another 1-2 fps from there being more 'air molecules' available closer to the seat? Eh...maybe, at best.
The air within the valve is like a spring decompressing as you create lift...and according to all my calculations, you have to worry about systematic pressure drop / avg pressure drop as a whole, not at one particular moment in time or space within the valve...
Plus as stated earlier, I have valves here in hand that are bored out to .5" within valve, and ported near equal to current valve, and with their volume increase, they are still out performed by a simple .005" difference in porting.
I just didn't want this information to go forward without being addressed as I feel its misleading. I would PREFER to be wrong here. Who doesn't want a potential 3-10% increase in fps? That is what the tinkering game is all about!
Kudos on the rest of your accomplishments thus far Scotchmo, I cannot say I am not a little bit jealous with what you accomplished via electronics! You have truly impressed myself and others with some of your work. Keep it up!
Fwiw I've used 25 gr hammers hitting the valve at 10 m/s, and my current 50 gr hammer that hits it at 6 m/s....and neither provide any significant gain over one or the other in terms of energy output, or efficiency. I don't see how an electronic hammer would provide any significant change while it generates lift...
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I think my suspicions are cleared up now, thanks guys...
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Fwiw I've used 25 gr hammers hitting the valve at 10 m/s, and my current 50 gr hammer that hits it at 6 m/s....and neither provide any significant gain over one or the other in terms of energy output, or efficiency. I don't see how an electronic hammer would provide any significant change while it generates lift...
As I said, I don't believe it would help every system, but in my case, there was a significant increase and I'm just trying to come up with a reasonable explanation as to why.
Some more info on differences of electronic valve:
The electronic valve is actually a "hybrid" that has aspects of the kinetic hammer. The difference is that it can maintain a 50-80lbf that continues to push on the valve stem even after the valve is open and hammer is static. The length of that duration is controlled by the capacitor charge supplying current to the solenoid. The time constant is the time needed to use up most (63%) of the stored capacitor energy. The RC circuit (solenoid and capacitors) currently has a time constant (tau) of .0015seconds for the single 2200uf capacitor. The hammer has not even reached the valve stem yet. Like a free flight hammer with most of the stroke used up by free flight. There is barley enough kinetic energy to open the valve at 3000psi. The best settings are +1 and +2. At +3 setting (2200uf +3x2200uf), the 8800uf has a tau of .006 seconds (about half of that time is used up for hammer acceleration, not valve duration). +3 is only for the heaviest pellets (34gr), otherwise that's too much time to keep the valve open and wastes air (and the loud bark confirms it). The electronic hammer is more like a hammer spring with enough preload to hold the valve open, and that preload can be removed after a couple of msecs allowing the valve to reclose.
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The electronics have evolved some since the original picture. There are now two electronic boxes. The left box is the main control, and that is all you need if you size the capacitor for one specific tune. The right secondary box allows you to easily switch capacitance in and out of the circuit in order to test various tunes. There is now a relay in the main box that latches the trigger switch on. I had tried a timed circuit to delay the release, but could not get it to work right. The relay addition was needed for when higher values of C1 were used - and the trigger release could happen before the capacitor was drained sufficiently to reset the SCR. Each shot now requires a cycle of the on switch. The latching relay also prevents the user from accidentally doing a double fire of the hammer.
(http://www.scotthull.us/photos/Armada/schematic-07.jpg)
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You're differentiating your pcp rifle from mine (electronically driven hammer versus conventionally sprung hammer) as if they're two entirely different kinds of systems that would respond differently to the exact same modifications (boring of valve near seat)...I really fail to follow your logic...
I could probably gather this info reviewing the entire thread, maybe not, so I'll just ask. What porting are you running on that valve and if regulated what plenum volume? Stock marauder length barrel? I would like to better understand the phenomenon of you gaining 30, 40, 60, or 100 fps by increasing amplitude of the impulse behind the projectile by means of increased volume near the seat as opposed to just any volume increase in general and removing possible restrictions in the system. I'm a numbers guy so, yeah...
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You're differentiating your pcp rifle from mine (electronically driven hammer versus conventionally sprung hammer) as if they're two entirely different kinds of systems that would respond differently to the exact same modifications (boring of valve near seat)...I really fail to follow your logic...
I could probably gather this info reviewing the entire thread, maybe not, so I'll just ask. What porting are you running on that valve and if regulated what plenum volume? Stock marauder length barrel? I would like to better understand the phenomenon of you gaining 30, 40, 60, or 100 fps by increasing amplitude of the impulse behind the projectile by means of increased volume near the seat as opposed to just any volume increase in general and removing possible restrictions in the system. I'm a numbers guy so, yeah...
I'm not saying that it is the electronics that is necessarily the difference in results, between you and I. I'm giving that information about the hammer operation so you can make your own evaluation. For a valve that opens slower, proximity of the impulse volume would be less critical. Do you believe the proximity of the plenum volume to the valve seat makes no difference?
Here are the other numbers that you can compare to yours. Valve as currently installed:
0.25"" throat
0.125" stem
0.196 diameter transfer port path
4 radial ports on thimble, 0.098" diameter each
~230cc total plenum @3000psi
28.3" barrel length
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My friend, John B. has developed some processes for investment casting from 3D models. He has a greed to work with me on a project that will look something like what is shown in these half section views that show the internals:
(http://www.scotthull.us/photos/Armada/valve-00.jpg)
(http://www.scotthull.us/photos/Armada/valve-01.jpg)
(http://www.scotthull.us/photos/Armada/valve-02.jpg)
The goal is to maximize the internal volume of the valve. There will be some minor changes to this first concept in order to work within the limitations of the production process, but it will be close to what you see here.
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Huh, so according to my calculations, you should be spitting the 34 gr at 2000 psi around 1002 fps / 76.5 fpe...and at 3000 psi with all that you should be screaming them well into the 1100's at 98 fpe...
And those calculations do not require any interior valve work other than what you have mentioned with porting, barrel length, plenum size, caliber, pellet weight and pressure...all they require is those numbers you give be true.
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Scott, all I can say is don't get obsessed with internal valve volume.... As long as the passage between the plenum and the valve, and the area to flow air around the poppet to the valve seat, are maybe twice the throat area you won't gain any significant power (if any) after that.... As long as the air can move towards the valve seat easier than it can pass it and travel through the ports.... there is really nothing more to be gained.... The concept of "more air on deck" near the seat doesn't matter if that air can be replaced quicker than it is being used.... Don't forget that in the first stages of opening the valve the area between the poppet and seat is tiny, and with the pellet basically not moving, there is no massive airflow around the poppet and through the seat, so no major pressure loss in the valve.... providing the air can be replaced easily from a large enough plenum....
A decade ago, when I worked on my first PCP, which was a Disco, I bored out the valve and got minimal gains.... When I discovered that the limiting factor was the hole through the gauge block, which was causing a pressure drop inside the valve, and enlarged that to bigger than the valve throat, the gains were FAR superior than anything from boring the valve.... It made so much difference just allowing more air into the valve that on future valve mods I didn't bother boring out the valve and saw no loss in power.... This was all part of the learning experience that led to my suggestion of 1 cc per FPE for the plenum volume....
Bob
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To be fair...before I put much thought or math behind it, I thought it was possible that the air within the valve of a pcp could displace itself faster than it could equalize, even with no air flow restrictions. Once I started doing the math, and viewing the operations during the shot cycle of a pcp thru a different lens, I understood better...
The operation of our valves are generally 1-2 ms (1 ms per foot of barrel isn't a bad rule of thumb for our commonly shot projectiles), and best viewed in micro seconds, so 1000-2000 micro seconds...which our brains truly have trouble understanding. Something happening 1000 times in 1 ms...or worse, a nano second, which occurs 1,000,000 times within that ms...good luck truly grasping that.
Of course you understand that to some degree working with the electronically driven hammer and manipulating the dwell within those orders...but if you try to spend some time understanding the trillions of interactions that occur within your valve in that 1-2ms time period, you'll understand that your diagram showing the importance of available volume being closer to the valve seat less appealing than simply ensuring you have sufficient volume to minimize overall pressure drop during that 1-2 ms cycle, as well as adequate cross sections for their flow paths.
To make it very simple, as long as your pressure into the valve, can meet or exceed the flow rate of the pressure out, you will never see significant losses due to air displacement near the seat...
-Matt
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.... As long as the passage between the plenum and the valve, and the area to flow air around the poppet to the valve seat, are maybe twice the throat area you won't gain any significant power (if any) after that....
Bob
The smallest passage to the bulk of the plenum is the gauge block. Was 0.375" dia, now 0.563" dia, in both cases over twice the throat area. I agree with Matt, that given the other parameters, I should be putting out significantly more FPE. I should be near 100fpe. What is your guess for as to where the limitation might be at this point?
Even if the increased valve volume will not help this rifle project, I still want to do the investment cast valve body as it will be an interesting endeavor that can be used on other projects including another gun of mine (a pistol that has an in-tube regulator with limited plenum space).
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Why the ball shape after the poppet?
If you want more fpe, you need a larger valve and ports, or you can move the valve closer to the pellet by moving it up in the picture, making it off center.
Simple radius at the corner will do, no need for ball shape.
And to maximize valve flow, make a radius seat for the valve, you gain much more flow vs valve lift.
Marko
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I would look at your radial barrel porting.... Four small ports, although they may be equal in area, will not flow the same as one large one.... particularly with the twists and turns in the flow path to the side and top ports....
Bob
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Your hammer weight (40gr) is WAY light for this kind of power/energy level imo, certainly for a conventional valve...I recommend .75gr to .85gr per fpe for your application (49-64 gr if you were to tune to 75 fpe) so basically closer to stock than you are now....this is even more necessary being you're using electronically driven means, as to aid in keeping the requirements there within reason...
I believe, based on some rough estimates I ran last night, you need roughly 2 ms dwell time and .16" lift, so ensure you have at least .16" of stem sticking out the rear of the valve...that .16" is wildly approximated so take it with a grain and use it as insurance that you don't need more than that, and that you want that at least available...
Perspective for you, even with the balance valve, you were still way under performing in terms of energy output for your arrangement of porting, barrel size, volume, and pressure....
Between that and the radial porting (likely less of the issue than the aforementioned) you definitely have some bits and pieces not lining up right to produce maximum energy for your particular build, and chasing more power by means of volume inside the valve when you already have 230 cc available is not going to be as productive as you think.
All laminar flow is born equal, but not all turbulent flow is...people seem to forget that all the time when stating "well the flow isn't laminar anyhow so who cares about some turbulence here or there"...so minimizing turbulence is still very critical...once that air hits the base of the pellet and travels down the barrel some it smooths out anyhow, but for 'valve flow efficiency', turbulence within is certainly attributable to loss in performance.
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Can you provide some details on your fpe calculations Matt? i like to calculate what my max fpe potential too
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Can you provide some details on your fpe calculations Matt? i like to calculate what my max fpe potential too
Its available in my signature, and fully transparent being google sheets with no hidden formulas. Its similar to Bobs Lofty FPE Formula, except instead of using your initial pressure, it uses your average shot pressure during the shot cycle, which also takes into account your transfer port waste. Instead of using 50% of your barrel volume, it subtracts your transfer port volume from that 50% and uses the remainder... Then the formula takes more loss consideration based on your porting, which technically is another reduction in average pressure during the shot cycle...and lastly it allows you to remove various losses (projectile break force, friction, valve flow efficiency, bolt probe flow efficiency) as a raw loss in overall %, which I find generally varies between .2% to 2% depending on the system. It is a work in progress (I'm not actively working on it now) so its evolved a lot since its inception..but I like to add to it from time to time or make minor changes, for example the version I am currently working on is a little bit different than the one available in my signature as I am using port size loss as a function of pressure loss as opposed to overall loss as seen in the current iteration. (which only changes the output roughly .5%, but I find it likely to better represent things from perspective of pressure drop from seat to muzzle)
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...with me currently making 64 fpe at 2000 psi and 80 fpe at 3000 psi shooting 34 gr...
...you should be spitting the 34 gr at 2000 psi around 1002 fps / 76.5 fpe...and at 3000 psi with all that you should be screaming them well into the 1100's at 98 fpe...
Why is yours only producing 80fpe, and not 98fpe as your ports are even larger (.225" on yours vs .196 on mine)?
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...with me currently making 64 fpe at 2000 psi and 80 fpe at 3000 psi shooting 34 gr...
...you should be spitting the 34 gr at 2000 psi around 1002 fps / 76.5 fpe...and at 3000 psi with all that you should be screaming them well into the 1100's at 98 fpe...
Why is yours only producing 80fpe, and not 98fpe as your ports are even larger (.225" on yours vs .196 on mine)?
19.5" barrel vs 28.3" ::)
19.5" barrel making 80 fpe is 4.1 fpe per inch of barrel, quite impressive actually.
28.3" barrel making 98 fpe is 3.46 fpe per inch of barrel...and that difference is due to your porting. ;D
Further, if I were to slap your 28.3 barrel onto my .225 ported lower, I would make 100 fpe..with my current 53 cc plenum, and then...going from 53cc to 230cc, I would then go up to 108 fpe...all calculated at 3000 psi, and only shooting 34 gr
Now its true peak fpe, with 1/2 gr per fpe...would be 148 fpe, shooting a 74 gr, with your configuration and my porting....let that soak in
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Why the ball shape after the poppet?
If you want more fpe, you need a larger valve and ports, or you can move the valve closer to the pellet by moving it up in the picture, making it off center.
Simple radius at the corner will do, no need for ball shape.
And to maximize valve flow, make a radius seat for the valve, you gain much more flow vs valve lift.
Marko
The throat is currently at 1/4" diameter. The spherical cavity is 0.32" diameter. That will allow the throat to easily be enlarged to 5/16" if the need arises. With a simple drill operation and no walking of the bit. I'll likely flatten the spherical cavity a little in the next design iteration (before actually building one).
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...with me currently making 64 fpe at 2000 psi and 80 fpe at 3000 psi shooting 34 gr...
...you should be spitting the 34 gr at 2000 psi around 1002 fps / 76.5 fpe...and at 3000 psi with all that you should be screaming them well into the 1100's at 98 fpe...
Why is yours only producing 80fpe, and not 98fpe as your ports are even larger (.225" on yours vs .196 on mine)?
19.5" barrel vs 28.3" ::)
19.5" barrel making 80 fpe is 4.1 fpe per inch of barrel, quite impressive actually.
28.3" barrel making 98 fpe is 3.46 fpe per inch of barrel...and that difference is due to your porting. ;D
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Good to know that I should be able to make 98fpe even with .196" porting.
Regardless of porting, when going for a high power tune, the longer barrel will definitely give less "projectile FPE" per inch, as it is also accelerating a greater total mass. Even at 1000psi, the the 28.3"barrel has about 7gr more mass of air to accelerate.
After spending several hours today, shooting at 50, 75, and 100yds, I'm finding I can't make use of any extra FPE anyway. 34gr pellets are still no good at any velocity. The most accurate pellet (though more susceptible to wind), was the 18.13gr. I had to reduce reg pressure down to 1800 psi (low as it would go) and I reduced the solenoid voltage from 60v down to 45v, and ran the capacitance at 4400uf. I got good results shooting the 18.13gr between 920 and 960fps. I experimented a little with the tensioned barrel and harmonics - and it looks like I'll need to do some more experimenting. I plan to try some muzzle weight additions next time.
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...with me currently making 64 fpe at 2000 psi and 80 fpe at 3000 psi shooting 34 gr...
...you should be spitting the 34 gr at 2000 psi around 1002 fps / 76.5 fpe...and at 3000 psi with all that you should be screaming them well into the 1100's at 98 fpe...
Why is yours only producing 80fpe, and not 98fpe as your ports are even larger (.225" on yours vs .196 on mine)?
19.5" barrel vs 28.3" ::)
19.5" barrel making 80 fpe is 4.1 fpe per inch of barrel, quite impressive actually.
28.3" barrel making 98 fpe is 3.46 fpe per inch of barrel...and that difference is due to your porting. ;D
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Good to know that I should be able to make 98fpe even with .196" porting.
Regardless of porting, when going for a high power tune, the longer barrel will definitely give less "projectile FPE" per inch, as it is also accelerating a greater total mass. Even at 1000psi, the the 28.3"barrel has about 7gr more mass of air to accelerate.
After spending several hours today, shooting at 50, 75, and 100yds, I'm finding I can't make use of any extra FPE anyway. 34gr pellets are still no good at any velocity. The most accurate pellet (though more susceptible to wind), was the 18.13gr. I had to reduce reg pressure down to 1800 psi (low as it would go) and I reduced the solenoid voltage from 60v down to 45v, and ran the capacitance at 4400uf. I got good results shooting the 18.13gr between 920 and 960fps. I experimented a little with the tensioned barrel and harmonics - and it looks like I'll need to do some more experimenting. I plan to try some muzzle weight additions next time.
Hmm, well, according to my calculations, a 28.3 barrel with my porting would do the 148 fpe with 74 gr, making 5.22 fpe per inch of barrel, where as with a 19.5 barrel that would be severely reduced to 100 fpe with a 50 gr....and that is 5.12 fpe per inch of barrel...
You shouldn't lead with so many assumptions, longer barrels do not suffer from what you state until their length becomes cumbersome in the sense that they induce friction and therefore do more harm than good....
And after reviewing your post, it seems as if you're shooting a .22 cal if you are mentioning 18.1 gr? I was under the impression you were a .25 cal since you mentioned 34 gr (not common that people shoot this in .22...)
I am confused....so if you're in .22 cal, you should be therefore limited to around 90 fpe at 3000 psi with the 34 gr (1090 fps)
(Even I am prone to make poor assumption ;D )
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Hmm, well, according to my calculations, a 28.3 barrel with my porting would do the 148 fpe with 74 gr, making 5.22 fpe per inch of barrel, where as with a 19.5 barrel that would be severely reduced to 100 fpe with a 50 gr....and that is 5.12 fpe per inch of barrel...
You shouldn't lead with so many assumptions, longer barrels do not suffer from what you state until their length becomes cumbersome in the sense that they induce friction and therefore do more harm than good....
And after reviewing your post, it seems as if you're shooting a .22 cal if you are mentioning 18.1 gr? I was under the impression you were a .25 cal since you mentioned 34 gr (not common that people shoot this in .22...)
I am confused....so if you're in .22 cal, you should be therefore limited to around 90 fpe at 3000 psi with the 34 gr (1090 fps)
Now you are changing the pellet mass as well as the barrel length. 74 gr vs 50gr, apples to oranges. The 74gr has a higher "projectile FPE" per inch than the 50gr, because the air mass is a smaller percentage of the total mass. I hope you can see that.
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Did you not read the title of the thread before you started posting?
"HP .22 design/build"
Read the posts in the thread and maybe you won't be "confused".
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Hmm, well, according to my calculations, a 28.3 barrel with my porting would do the 148 fpe with 74 gr, making 5.22 fpe per inch of barrel, where as with a 19.5 barrel that would be severely reduced to 100 fpe with a 50 gr....and that is 5.12 fpe per inch of barrel...
You shouldn't lead with so many assumptions, longer barrels do not suffer from what you state until their length becomes cumbersome in the sense that they induce friction and therefore do more harm than good....
And after reviewing your post, it seems as if you're shooting a .22 cal if you are mentioning 18.1 gr? I was under the impression you were a .25 cal since you mentioned 34 gr (not common that people shoot this in .22...)
I am confused....so if you're in .22 cal, you should be therefore limited to around 90 fpe at 3000 psi with the 34 gr (1090 fps)
Now you are changing the pellet mass as well as the barrel length. 74 gr vs 50gr, apples to oranges. The 74gr has a higher "projectile FPE" per inch than the 50gr, because the air mass is a smaller percentage of the total mass. I hope you can see that.
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Did you not read the title of the thread before you started posting?
"HP .22 design/build"
Read the posts in the thread and maybe you won't be "confused".
Certainly...I will gladly admit to my mistake...I overlooked the title and based an assumption on your projectile weights. I think its clearly less of a fault then what we're discussing here, but if that's where you want to focus on, I'll simply smile and say, at least I am humble enough to accept my mistake and learn from it, hope you'll do the same ;)
Further, I changed projectile weights so both configurations were shooting 950 fps, which equates to 1/2 gr per fpe...apples to apples, follow along now.
Ps. Cherry on top, I identified my mistake myself, and corrected...myself...so it looks like I am correcting both your and my mistakes, you're welcome.
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I would look at your radial barrel porting.... Four small ports, although they may be equal in area, will not flow the same as one large one.... particularly with the twists and turns in the flow path to the side and top ports....
Bob
I realize that the radial ports will likely not flow as well as one large port of equal area, but I like the smooth feeding of all types of pellets, so the radial ported thimble will stay for now.
Though with the current higher FPE, the radial ports could indeed be the new bottleneck. The radial ports were not the bottleneck before as I was able to get the FPE up considerably via changes to the valve body.
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Scott, when you go higher in fpe. if the pellet dont group, try slugs. it will be a slight reduction in fpe but it will be so satisfying if a slug can touch something at 75-100yards.
you probably want to make another thimble with 1 port to find out what you could gain in fpe vs radial ports..196 will still be smooth enough for pellets, certainly fine for slugs.
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Scott, I have not yet been able to get any accuracy with the 34 gr. Beasts.... However the 25.4 gr. Redesigned Monsters can shoot as well as the 18.1 gr. Heavies....
Matt, if you can get 148 FPE in .22 cal from a 28.3" barrel at 3000 psi I would gladly bow to your superior ability.... Heck, I will shout your praise from the rooftops.... ;)
Bob
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Scott, when you go higher in fpe. if the pellet dont group, try slugs. it will be a slight reduction in fpe but it will be so satisfying if a slug can touch something at 75-100yards.
you probably want to make another thimble with 1 port to find out what you could gain in fpe vs radial ports..196 will still be smooth enough for pellets, certainly fine for slugs.
The 27grain NSA slugs also did well. I built this gun primarily to shoot in extreme benchrest type matches. and as of yet they do not allow "slug" shapes. The pellet has to look like a Diabolo pellet. With all the major manufacturers now producing non-diabolos, hopefully the rules will catch up.
I have a single port thimble with a 0.156 port. It performed about the same as the 4-port radial thimble. When loading, I can feel some of the shorter pellets dipping already.
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Scott, I have not yet been able to get any accuracy with the 34 gr. Beasts.... However the 25.4 gr. Redesigned Monsters can shoot as well as the 18.1 gr. Heavies....
Matt, if you can get 148 FPE in .22 cal from a 28.3" barrel at 3000 psi I would gladly bow to your superior ability.... Heck, I will shout your praise from the rooftops.... ;)
Bob
I had some decent groups with the 25.39RD's but not yet consistently. I'll likely be testing them more when experimenting with the harmonics and muzzle weights. I need to look into it more, as some initial tests seemed to show worse accuracy when I increased the barrel tension past a certain amount. Tests were limited, so nothing for sure. I'm not yet convinced that a light weight, stiffened barrel is better than the heavy steel barrels that I have used before.
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I did some rough volume calculations on the valve body. The stock valve body has about 4cc of free volume. The bored out valve body in the gun now, is at about 11cc. The investment cast body will have about 18cc of free volume.
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Make 2 .... would love to test and see if or not your findings could become my findings too ???
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Make 2 .... would love to test and see if or not your findings could become my findings too ???
I know John tends to have a production oriented mindset when developing his processes. If the cast valve body works out, he will likely want to try casting some in batches.
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It's been awhile since I posted any progress.
John is still working out the casting details for the valve body. Lots of little problems to work out.
I have been playing with the barrel harmonics, using different muzzle weights and different tension amounts. Medium tension seems best and heavier muzzle weights seem best, but still not all that consistent. I'm going to replace the carbon fiber outer shroud with a heavy steel sleeve. It will add considerable mass (>3lb), but it's for bench rest, so not so bad. The barrel liner will still be in tension. I'll also try supporting the barrel liner in the middle with o-rings or something.
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I got the DOM tubing for the heavy steel barrel shroud. It will be used with a barrel liner that is NOT under tension. The difference will require a new breech, so that test has been pushed out some.
We worked out most of the build issues of the investment cast valve project only to find that the casting has significant porosity, and it leaks at a fairly high rate when subject to high pressures. We are looking at ways to seal them.
In the mean time, the harmonics experiments ended with me eliminating the resilient compression member and using a steel nut to tension the barrel liner. I added an o-ring to the middle of the liner's length to hopefully dampen the harmonics. A bushing of tape is wrapped on middle of the liner with an o-ring held in place and compressed slightly against the inside of the carbon shroud. Accuracy is at least as good as it was with the various harmonic weights.
The current tune works well with the reg set in the 2600-2800psi range. JSB 25.39 RD at 1050fps-1060fps. That gives me 62fpe-63fpe and about 50 shots on a 4500psi fill. Under various wind conditions, I'm getting about 30% of my 5shot groups under 1moa.
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The tensioned FX slug liner has been just OK. I'm going to be testing some more conventional barrels. The next barrel will be a 30" LW unchoked poly. 16mm diameter. In order to make barrel swapping easier, I'm designing a new breech block for the Armada. It will be a single/direct load only (no magazine). The barrel will be clamped into the breach using four easily accessible fasteners, and will not require any transfer port machining. Barrel diameter can vary from 14.9mm to 16.1mm. Barrel prep will be minimal (like a Thomas or USFT). The breech will slide side to side and will have full .250" porting and sufficient room to load/use pellet/barrels of .177 to .357 caliber. The initial test parts will be printed PLA, but I hope to cast them in aluminum eventually.
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Very slick .. very specialized for very special rifle that does not require a conventional cocking cycle.
I Like it !!
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Very slick .. very specialized for very special rifle that does not require a conventional cocking cycle.
I Like it !!
I plan on doing a version with a charging handle for conventional hammers.
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For when I want to try a conventional hammer:
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Good looking designs, nice to see something new being done.
Marko
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After several design iterations and five 3D prints, I have a breech that I will try out. I plan on using aluminum eventually, but for now, tests will be performed using the PLA breech. Early version had the loading port on the right side. I later moved the loading port to the left side which is more convenient for me as it is easier to see from most of my shooting positions. I used 0.3mm layer height in order to speed up the printing. Not pretty at this point, as for now I'm more concerned about function. I did include provisions for cocking a conventional hammer (see slot on right side). I'll test the breech first with my existing valve. For now, the porting in the breech will be a full 0.25" diameter from the valve to the barrel. That's a little large for my current valve (0.196" port), but will work better with the Cothran valve which I just ordered. I'm curious how the Powerhouse valve will respond to various settings for hammer dwell.
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very cool !
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I really like the design. I like the way it loads and transfers the air to the bullet base. It allows proper seating in the leade but doesn’t waste a lot of space.
Not to mention the design just looks nice.
I originally purchased my 3D printer to do some lost pla casting. Haven’t tried it yet.
I have a feeling the new valve will work with a lot less capacitance. And you can probably turn the voltage down a touch. Is that what you are predicting?
Dave
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I really like the design. I like the way it loads and transfers the air to the bullet base. It allows proper seating in the leade but doesn’t waste a lot of space.
Not to mention the design just looks nice.
I originally purchased my 3D printer to do some lost pla casting. Haven’t tried it yet.
I have a feeling the new valve will work with a lot less capacitance. And you can probably turn the voltage down a touch. Is that what you are predicting?
Dave
The Powerhouse valve is a "balanced" valve so it should open easier, but the larger stem diameter means that for a given pressure, it will also close easier/faster against the hammer. My thinking is that I will need to keep the voltage high in order to keep the holding force at maximum, but I will reduce the hammer stroke to just enough to crack the valve open. If there is sufficient solenoid force to continue to hold the valve open, I will use the capacitor switches to change the dwell time.
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Another iteration of the breech with integrated scope mounts at 20moa compensation. The bridge between the mounts stiffens things up a lot.
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Nice !!!
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Kewl! 8)
Jesse
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My friend and I are working to cast this breech in aluminum. The breech is longer than anything he has done with the lost PLA process. We needed a longer flask. I ordered a piece of rectangular steel tubing (2.5”x4”x10”long) as that is about the biggest that we could fit in his small oven and just big enough for the breech. The "flask" should be here in a week or so. In the mean time, I decided to keep working. The single load breech can have full size ports up to 1/4”, so I decided to order a Cothran Powerhouse valve to take advantage of that fact. In order to get a baseline, I bored out the Marauder valve until I had .218” porting from the .25” throat up to the pellet. I styled the transfer port interface after the Cothran valve in order to make the switch to the Cothran a simple switch out of valves. Today I tested with the ported Marauder valve. I was a little wary of running a PLA breech and pellet shuttle at high pressure. I started at 1200psi and saw no red flags. Then 2000psi, 2500psi, and up to 3000psi. The barrel started slipping at one point so I had to loosen the PLA clamps (final version will have steel or aluminum clamps) and re-seat the barrel, then re-tighten. The only broken plastic was when I left the breech shuttle open. It blocks the transfer port when open to load. When I fired with the open breech, the end broke off the shuttle and blew an o-ring. The broken shuttle was still usable and sealed fine when closed. I replaced the o-ring and continued with the broken shuttle taking more care to insure that it was closed before firing. The aluminum shuttle should be able to withstand errors such as that. I used JSB .22 Jumbo Beasts (34gr). The barrel is a 30” LW poly, unchoked. The sweet spot with full hammer voltage and capacitance was about 2800psi. There was a slight valve lock over that but it sounded noticeably quieter at 3000psi. The highest velocity was 1092fps (90fpe) at the muzzle. That beats the 79fpe that I got a few months back with the Motorhead balanced valve. I decided to run a 10 shot string to get some numbers. The gun was setup unregulated with the standard Marauder air tube filled to 3000psi.
JSB .22, Jumbo Monster, 34gr
L 1001 fps
H 1088
AV 1055
ES 88
SD 27
(3000psi)
1047
1075
1088
1078
1080
1061
1053
1041
1028
1001
(2100psi)
Assuming the GEN2 tube is 215cc capacity (not sure about that), I ran the numbers through the Lloyd Sykes efficiency calculator and got:
avg FPE/cuin per shot = 1.03
avg bar-cc/FPE per shot = 15.9
avg FPE per shot = 84.1
avg PSI used per shot = 90
I'm hoping that the Cothran valve gets me over the elusive (at least for me) 100fpe. Though, from what I've read, I'll likely be giving up the nice shot curve when unregulated. I should be able to get about 40+ shots with the 4500psi, 450cc bottle attached, and regulated to 3000psi.
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some serious power in 22.. im sure the cothran will put it over 100
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WOOF !!!! to be sure and in .22 caliber too 8)
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Awesome stuff! And looks great!
Fingers crossed for you with the Cothran as well, I bet it’ll do it.
Dave
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1156fps, 101 fpe at 3000psi
1197fps, 108 fpe at 3200psi
I installed the Cothran valve and filled the Armada air tube to 3000psi. I wanted to ease into the hammer strike to see how easily the valve opened compared to the old (non-balanced) valve. I stayed at 60v and started with the base setting (on with one default 2200ufd capacitor). I started with minimum stroke and increased the stroke until I started to get a good air blast (with no pellet). At max stroke (about 1/2"), still not much, so I engaged the next capacitor switch and got a good blast. I inserted a 34gr pellet and the first shot gave me 1138fps (98fpe). I refilled to 3000psi and engaged all capacitors (4 x 2200uf). Over 100fpe!...1156fps (101fpe)... As expected, the next shot from the unregulated tube was lower at 1141fps, and every subsequent shot was less than the previous. The old valve was maxed out on the hammer and any pressure increase beyond 2800psi reduced the velocity. The Cothran valve is still below the pressure limit of what I can open with my hammer. The Marauder tube is rated for 3000psi, but I felt OK testing a little higher pressure, so I filled to 3200psi: 1197fps (108fpe). I would need a higher pressure air tube to safely test the upper limits with this valve, but I'm already over what I expected.
I'm currently using Harbor Freight 70 durometer Nitrile o-rings. I plan on getting some higher quality 90 durometer o-rings, as these cheapies only last a couple of shots at 3000psi. They extrude out the gaps between the PLA breech shuttle and the back face of the barrel and transfer port tube. The planned aluminum shuttle should work better in this respect as well.
I know others have gotten 100fpe with .22 airguns, but usually with 40+gr slugs. I did it with a 34gr pellet. I'm kind of borderline as to getting much benefit from the Cothran valve. I hope to see bigger benefits from this valve when I test 40+gr slugs.
This breech design provides a fairly-open/fairly-short pathway from the valve to the barrel. The smallest restriction currently is the transfer port tube at .218" ID.
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While high numbers make headlines .... Using it in that caliber may prove an even bigger challenge ::)
Nice milestone never the less !!
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awesome , any sonic booms in there ? also , The pinning is the weakest part of that tube design , i think a hardware update and a steel front threaded cap would allow for 3600 fills.
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awesome , any sonic booms in there ? also , The pinning is the weakest part of that tube design , i think a hardware update and a steel front threaded cap would allow for 3600 fills.
I'm already able to exceed my original design goals (40gr@1060fps). I'll probably leave the tube as-is. The only required mod to the tube was to bore out the hole for the transfer port bushing to 7/16". Earlier, I had also drilled a hole for another breech hold down screw but no longer use it as the new breech design is much stiffer.
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While high numbers make headlines .... Using it in that caliber may prove an even bigger challenge ::)
Nice milestone never the less !!
True, but I now have a little leeway. I'll likely back off slightly once I get some 40gr slugs to test. The goal is 40gr slugs at 1060-1070fps. Thus equaling the performance of .22lr standard velocity ammo. And hopefully 30+ shots at that velocity with a 450cc bottle.
I just ordered (100) of the Griffin .217 boat tail 40gr.
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Congrats hitting the goal!
Dave
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The Cothran valve doesn't cycle normally without a pellet.... When properly tuned for a pellet, and then dry fired, you will just get a "pop" of air.... It's just the way that valve works.... Try detuning your hammer strike until you just barely see a velocity drop WITH a pellet in the chamber.... What you will likely find is that even a small decrease in hammer strike from there and the velocity will fall off a cliff.... The Cothran valve does not have a bell curve, the velocity drops with the pressure.... It is the most efficient tuned just above the cliff, but don't tune it too close to the cliff or the ES will be terrible.... Here is a typical plot of velocity and efficiency vs. hammer strike for a Cothran....
(https://hosting.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/.highres/DD%20Cothran%20Efficiency_zpsqzb8n5tb.jpg) (https://app.photobucket.com/u/rsterne/a/d8b60ed8-9651-478b-96e4-937970f0e59d/p/558225d4-41e9-4a82-9473-f19c7ae81452)
A plateau, and a cliff.... ::)
Bob
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The Cothran valve doesn't cycle normally without a pellet.... When properly tuned for a pellet, and then dry fired, you will just get a "pop" of air.... It's just the way that valve works.... Try detuning your hammer strike until you just barely see a velocity drop WITH a pellet in the chamber.... What you will likely find is that even a small decrease in hammer strike from there and the velocity will fall off...
I should have said a good "pop" of air, not "blast". I wanted to see max velocity settings. So I jumped over a middle setting (6600uf). I see that there was not much difference between 4400uf (1138fps) and 8800uf (1197fps), so if I were going to run it at this energy level, it would likely be closer to the lighter hammer strike. I ran low on 34gr pellets, so more testing later. I can fine tune between capacitor settings via voltage adjustment.
Bob, I'm glad that you chimed in as I have read all of your posts on your "Hayabusa" and experiments with the RWS 22lr slugs. That was a performance goal that I set early on for this build.
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exciting stuff! i am thinking slugs will go slower but hope you can achieve your goal!
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Awesome build Scott. Subsonic 22lr velocities from 3k and an electronic controlled valve . Call me impressed. I’ve got a few hundred of the RWS bullets and they are quite impressive. Except for the price.
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I got some 40gr Griffin boat tail slugs to test. Only change to the airgun was to reduce the 0.250 dia shuttle porting to 0.218 to match the transfer port diameter. That reduces the lost volume by a tiny amount but did not seem to make any significant change in performance. And the barrel o-ring is now 90 durometer polyurethane. I'll eventually replace the Buna transfer port o-rings with polyurethane.
215cc unregulated tube at 3000psi
Griffin 40gr .22
L 1011fps
H 1103
AVG 1058
ES 92
SD 38
3000psi
1103 fps (108 fpe)
1086 fps (105 fpe)
1056 fps (99 fpe)
1031 fps (94.4 fpe)
1011 fps (90.8 fpe)
2100psi
avg FPE/cuin per shot: 0.61
That's with only 5 shots and not a very accurate gauge, but obviously still on the very low side.
I tried +1, +2, and +3 settings on the hammer. All worked with almost the same fps, but the +1 did not always open the valve enough (sometimes OK, but sometimes only 380fps), so I went with the +2 setting where it always opened reliably. The Cothran Powerhouse valve gives me 15% to 20% more fpe than the ported Marauder valve, but it takes a big air efficiency hit (0.61 vs 1.03).
The power efficiency (delivered vs expected) is very good. The barrel_volume(1.1CI/12) x avg_psi(2910psi) energy is 269fpe. My pellet energy is 108fpe. That gives 108/269 or 40%. The "lofty goal" of 50% should be doable with a heavier pellet (assuming the valve has sufficient dwell for the slower pellet). Currently, the air mass that is being accelerated is over 60% of the total energy consumed. There are other losses but they are small compared to the air mass. My spreadsheet shows 66gr of air in the barrel after adiabatic expansion from the plenum outward. For a lofty goal of 50%, that energy used to accelerate the air can't be over 50% of the 269fpe that is available, or 134.5fpe. That means a 66gr pellet at 958fps. I think this gun is capable of that, except I'd probably need to get a 1:12 or 1:10 twist rate barrel for a pellet that long.
If I include all of the air mass, (66gr air + 40gr pellet, @1103fps), the power efficiency is 106% (286fpe/269fpe). That's an indication that not ALL of the air is moving at the same velocity as the pellet.
40gr@1060fps(100fpe), my original goal, is easily achievable with the Powerhouse valve. I still need to test it with the regulated bottle installed. Hopefully, I can get a decent shot-to-shot fps consistency.
The excessive air use of the Powerhouse valve is still a concern. Though I should still get 20 to 30 shots at 100fpe with the 4500psi, 450cc bottle installed. I don't see an easy way to get this valve to close sooner. Maybe the Powerhouse valve has a somewhat fixed dwell time. Slowing the pellet acceleration via a transfer port restriction might help.
I'm still using the PLA breech.
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very good data collection and all very impressive.. I wish i had a 3000 psi helium tank to send over, that would get real interesting .. Seems like between settings 1 and 2 is where the knee is , or rather the cliff.. You would need some other adjustment to augment setting 1 to find that sweet spot.
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very good data collection and all very impressive.. I wish i had a 3000 psi helium tank to send over, that would get real interesting .. Seems like between settings 1 and 2 is where the knee is , or rather the cliff.. You would need some other adjustment to augment setting 1 to find that sweet spot.
I can't augment the +1 hammer setting, but I can reduce the +2 setting. That will be easy enough with the voltage adjustment. Right now I have it set at max voltage (60v). I can turn the voltage down until it starts to go over the "cliff", and then turn it up a little more from there.
The 108fpe at 3000psi is too high anyway. I should be getting the desired 100fpe at about 2600psi. With a regulated bottle set at that lower pressure, +1 at 60v might be about right for the hammer.
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i forgot about the voltage adjustment, so its still infinitely tunable .. pretty wild.. And also demonstrates the potential of a PLA , abs , or a machined delrin breech.( as long as the loads are well planned,. as an aside , ive been doing some CAD quoting on Xometry for different ideas, and that breech might not cost much to outsource if done in plain 6061 ..If the file is uploaded as a step , the quote appears iin about 30 seconds , no commitment.. Its really interesting how fast theyre computer generates quote based on setups , size , material , and tolerances.
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I agree, sounds like you need something in between #1 and #2.... Find the cliff and then go up just a bit from there.... You should be able to get efficiency of over 1.0 FPE/CI....
Bob
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I agree, sounds like you need something in between #1 and #2.... Find the cliff and then go up just a bit from there.... You should be able to get efficiency of over 1.0 FPE/CI....
Bob
I will be playing with it quite a bit. At 3000psi/30" barrel/40gr/.22 slug. 108fpe at 1.0 FPE/CI would be great, but that's not necessary, and I'm not sure if it's even possible. If I could get it to do 1.0 FPE/CI at 100fpe, I'd be thrilled (probably a lower pressure would be used).
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The +1, 60v setting works reliably at 2750psi. I'm getting about 1070fps with the 40gr, and the air blast seems reduced. Without a slug, a quick "pop" of air. If I reduce the pressure much further or increase the hammer hit, there is a "blast" of air, even without the slug. It seems that increasing the capacitance is increasing the hammer hit as well as increasing the dwell, even though I don't need a longer dwell with the Cothran valve. All pretty much as expected I guess.
I have the regulated bottle installed now. I tested several slugs at +1, 60v, and 2750psi:
32gr cup base, .217" - 1158fps, 95fpe
32gr cup base, .218" - 1170fps, 97fpe
40gr BT, .217" - 1079fps, 103fpe
44gr BT, .217" - 1038fps. 105fpe
Next tests will be to shoot at some 75/100yd targets, tomorrow I hope.
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Reads like your getting it where you wanted all along ... nice work Scott
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Reads like your getting it where you wanted all along ... nice work Scott
Exactly what I wanted for fpe and velocity.
I got up to Cambria this afternoon to test the barrel. I had planned on shooting out to 100yds but that did not happen. Cool but no wind today. I did get out to 55yd. I got excited with the first 5 shots of 40gr BT @1070fps. First and second shot were same hole, so I thought I was missing. Next shot same ragged hole. 0.16" CTC. I re-zeroed closer to the bullseye and two shots 0.17" CTC. Then I forgot to close the breech and blew out the t-port, o-rings, and shuttle/slide (for the second time since!). The slide literally went over the cliff, so I decided not to look for it. I did find the transfer port as it bounced off John's forehead. Could have been a bad situation. The intent of the design was to have the slide blocking any air from coming out if fired while open. But it can't handle the pressure so it breaks. John suggested drilling a vent hole so that the air can escape if it's fired while open. I'll do that on the next plastic one. I might wait for the aluminum version due next week maybe.
Those five shots look promising but not enough for anything definitive. The lack of wind made for unusual conditions so not a good comparison to what I've gotten in the past. I'll need to test more and in the wind.
It's an air hog. It looks like it might be good for only 12 shots in it's present configuration/fpe. I am considering slinging a 1.1L CF tank to replace the 0.45L aluminum tank. It would fit OK just with a new hanger bracket. That should give me about 30 shots.
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Nice progress, and good number.
Ditch the plastics as you evidently are going to blowup something.
Don't mind that the gun is "air hog" it's not even close. Just shoot and enjoy if it works. Air is readily available still. ;D
Marko
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i forgot about the voltage adjustment, so its still infinitely tunable .. pretty wild.. And also demonstrates the potential of a PLA , abs , or a machined delrin breech.( as long as the loads are well planned,. as an aside , ive been doing some CAD quoting on Xometry for different ideas, and that breech might not cost much to outsource if done in plain 6061 ..If the file is uploaded as a step , the quote appears iin about 30 seconds , no commitment.. Its really interesting how fast theyre computer generates quote based on setups , size , material , and tolerances.
I put in an RFQ with Xometry. I requested DMLS (Direct Metal Laser Sintering) in aluminum. They can't do the automated quote for a part that large, so I am awaiting a manual quote.
Nice progress, and good number.
Ditch the plastics as you evidently are going to blowup something.
Don't mind that the gun is "air hog" it's not even close. Just shoot and enjoy if it works. Air is readily available still. ;D
Marko
I'm not too worried about blowing up the breech as the only PLA part with significant HPA flowing through it is the slide. I remade the slide with an "open breech vent hole" and tested it. Now when I leave the breech open, air blows out but everything stays in place. Currently, the scope mounts are also PLA. The dimensional stability of PLA is OK but not great. PLA is especially bad when subjected to heat, so aluminum would be preferred.
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Nice Scott. i have an order in with them as well for some machined 6061.Just a batch of stuff i dont wanna make and a few friends want .. they were able to do the automatic quote as i didnt request special finish or threading.( ill do all the threading myself ) .When i added any option outside of plain finish , i needed a human review so i skipped it this time.. The cintered aluminum should be pretty cool. Be curious to see the fininish they can put on it
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The vent hole in the slide did not work. The hole relieves pressure faster but it weakens that part of the slide by 30%. I tried it once with an open breech and it held once, but not a second time. The vent time is brief but it still needs to hold back 300lbf while venting. I'll make the next slide out of 1018 CRS which is almost 10x stronger than the PLA.
The aluminum breech via lost PLA is still in the works.
No luck with Xometry yet. Xometry does not think the geometry would work well with DMLS aluminum printing, but they are looking at other options.
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always the option to have it machined, but after running some quotes for single items , i can say it gets quite expensive..I found that 20 is the magical number of items where the price per unit starts to make sense.. Granted , ive only uploaded 5 models or so
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If you can print it and they think they cant do it with powder bed metal printer, find another company.
Clearly they have no idea what they are doing!
Marko
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i looked into a quotes on xometry for a machined part versus cintered .. both in aluminum.. the printed dmLS part was 10 times the price.. crazy stuff.
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hey SCott, my machined parts from xometry came in , they look incredible.. I added no finish at all , just machined parts and they look great.. if you want a pic PM me . But otherwise , ive gained a lot of confidence in them. also , i had tolerances set at +-.005 , everything is withiin .0015
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hey SCott, my machined parts from xometry came in , they look incredible.. I added no finish at all , just machined parts and they look great.. if you want a pic PM me . But otherwise , ive gained a lot of confidence in them. also , i had tolerances set at +-.005 , everything is withiin .0015
No luck getting xometry to quote that part. I'm continuing development. John did a trial casting of the breech and it is almost usable. Though since then I have changed the design some. I changed the shuttle/slide so that it is stronger, and changed the loading method to include a built-in pellet seater.
It's a process with multiple iterations. Here are a few variations including the first aluminum test part:
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the casting looks great ..Needs a referencing surface for reaming , threading , cleanup . etc.. maybe the top of the scope rings. Making a fixture for it would be an entirely new adventure .. CAsting is probably the best way to make those/ Unless someone has a 5 axis and a decent amount of spare time. (-'
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the casting looks great ..Needs a referencing surface for reaming , threading , cleanup . etc.. maybe the top of the scope rings. Making a fixture for it would be an entirely new adventure .. CAsting is probably the best way to make those/ Unless someone has a 5 axis and a decent amount of spare time. (-'
The holes are already cast in, so a fixture is not really needed. I re-drill with a hand drill to clean them up. On the exterior, I knock off high/rough spots and flat surfaces with a file. Curved surfaces with sand paper. Tap the threaded holes and it's ready to go. Same process that I use with the printed PLA parts.
A note on threaded holes: Though I use cutting taps for the aluminum parts, PLA does better with a thread forming tap on smaller holes (1/4" and smaller).
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sounds good to me .. i figured the barrel hole and bolt path would need reaming , but i dont know a think about how clean a casting can be made.
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sounds good to me .. i figured the barrel hole and bolt path would need reaming , but i dont know a think about how clean a casting can be made.
Investment casting is much more precise than sand casting. You can eliminate many secondary operations that would be required to finish a sand casting. There is not really a "bolt" path with this design. At least not for the version with the solenoid hammer. The shuttle/slide area could be broached but it's at least $150 for a 3/4" broach. I cast the "runway" to size and I use a flat file on the four interior sides to clean it up. Since the barrel clamps in place, I made the barrel hole slightly oversized (0.645" dia). I ream the main hole with a 41/64 drill bit and that cleans up any burrs or high spots.
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I'm testing out different t-port sizes to see how it affects the Powerhouse valve as far as efficiency. I'm leaving the pressure at 2600psi for now.
Port size, approx FPE
0.250 - 100 fpe (40gr@1060fps)
0.140 - 54 fpe (25.4gr@980 fps)
0.125 - 42 fpe (25.4gr@860 fps)
I also ordered a 36" TJ 25-20 liner, and an Arsenal 257420 BT mold. I'll be using them with this gun later on.
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36 incher !!!! wow .,this thing will be cooking .. those transfer port numbers are quite dramatic , moreso than i expected for a smaller caliber
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Not too far off the FPE being proportional to the port diameter.... as I have been using for estimating FPE for a long time.... 8)
Bob
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First cast breech was unusable, second was barely usable. Third try and we got an OK casting. Still some troublesome defects but nothing major. The furnace (for PLA burnout and aluminum melting) is just not big enough for the volume needed. We are working on a bigger furnace. In the mean time, I'll use this cast breech.
I got the .257 barrel prepped and installed. I'd already done a little testing of the barrel. With 82gr slugs, 3000psi, 966fps, 166fpe. I have not reamed the chamber yet, so I had to drive the slugs in. Even without any chamber preparation, pellets actually fit the barrel OK. So I now have it setup to shoot 34gr JSB pellets, 1800psi, 1085fps, 89fpe. I will be testing it on Monday in the pellet configuration.
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That’s gonna be sweet when you get it all dialed in. I just ordered a 36” .257 as well. I’ll be watching your development on this.
Congrats on getting the casting useable.
Dave
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Nice work on the casting and design!
I like the way you incorporate the scope mounts in to the receiver.
Bigger valve way bigger transfers than caliber works wonders for power, there is no wasted volume when considering power.
The more air you get behind the pellet as fast as you can just matters.
Marko
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Nice work on the casting and design!
I like the way you incorporate the scope mounts in to the receiver.
Bigger valve way bigger transfers than caliber works wonders for power, there is no wasted volume when considering power.
The more air you get behind the pellet as fast as you can just matters.
Marko
Bigger transfer than caliber? Does not seem that there would be much/any gain by going over caliber. As long as the pathway equals caliber area from the throat to pellet, flow is about maxed out.
I just tried some 73gr RL 257420 slugs over the chronograph. Full ports at 3200psi averages 1058fps, 181fpe.
That's already at/near the maximum theoretical velocity of this configuration at 100% efficiency for total kinetic mass (air + pellet).
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Oh so you are at 100% theoretical efficiency. At what part of the barrel?
Probably breach end, what about the other end, you are down at 50% again?
The air mass is reducing as the bullet advance in the barrel.
I'm at 62% at the muzzle.
What do I know...
Marko
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What do I know...
More than anyone else that has ever built an airgun, you have proven that many times.... 8).... I look forward to the days when your vast knowledge is commonplace, and people can throw away my "lofty goal" as ancient history.... All it takes is generously sharing and explaining your knowledge, in detail, so that everyone else can benefit....
When working with a long barrel, I would be surprised if Scott's build gets to 50% of theoretical, but I certainly hope he does.... The shorter the barrel, the less air in it, which makes it easier to break that 50% of the theoretical FPE ending up in the bullet.... If the air mass exceeds the bullet mass, IMO that becomes virtually impossible....
Bob
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Scott, correct me if I am wrong.... but your barrel is 36", right?.... That makes the theoretical FPE [ (0.257^2 x PI/4) x 3200 ] x 36/12 = 166 lbf. x 3 ft. = 498 FPE.... and my "lofty goal" would be half that, or 249 FPE.... If you are over 180 FPE (and well over 950 fps), you would get closer by using a heavier bullet, about 90 gr. should put you at (or over) 950 fps (which is where my loft goal is intended to be used).... That increases the bullet mass as a percentage of the total, and should push the FPE higher.... It would be interesting to see what you would get with a 100 gr. bullet, I would think 200 FPE is within reach....
Exceeding the 50% goal can be done by using a heavier bullet.... This is because it changes the ratio of bullet mass to total mass of bullet plus air.... Air at 3200 psi weighs about 64 grains per CI.... Your barrel, at that pressure, contains about 120 gr. of air.... So, at least in theory, it might take a 120 gr. bullet to get to 50% of the theoretical maximum.... This also explains why short barrels can help exceed the 50%.... They contain less mass of air, so the bullet becomes a larger percentage of the total mass.... I have said before that I should probably revise my lofty goal formula to take this into account.... but when nobody except Marco gets there, it seems kind of pointless.... Still, I may do that someday, just because.... ;)
IMO, you have done a great job on your build.... Congratulations.... 8)
Bob
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I do share, but you need to read it between the lines, porting and pictures have been in the forum innthe lucky shot thread. Four ports in the barrel, valve dimensions have been told couple of times.
What I have not told is barrel is special, its tapered for easy starting of the movement. First 150mm is very loose and tapers to nominal dimensions after that, slightly tapering to the muzzle.
Its like drag racing, you loose the most time at the first quarter of the strip.
Marko
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What do I know...
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When working with a long barrel, I would be surprised if Scott's build gets to 50% of theoretical, but I certainly hope he does.... The shorter the barrel, the less air in it, which makes it easier to break that 50% of the theoretical FPE ending up in the bullet.... If the air mass exceeds the bullet mass, IMO that becomes virtually impossible....
Bob
To me, theoretical maximum FPE is:
(air_pressure x barrel_volume x projectile_mass/(projectile_mass + air_mass)
Since I will be using a 70gr-73gr slug (depending on lead composition), I won't be over 40% of your "Lofty Goal" as it is theoretically impossible to do so. If I wanted to get a 50% lofty goal, my pellet mass would need to equal the air_mass. There is no way around that fact.
I'm already really close to my realistic goal.
The maximum projectile length that my current breech easily accommodates is 0.750". That is about the longest I want to use for optimal stability in my 1:14 twist rate barrel.
Scott, correct me if I am wrong.... but your barrel is 36", right?.... That makes the theoretical FPE [ (0.257^2 x PI/4) x 3200 ] x 36/12 = 166 lbf. x 3 ft. = 498 FPE.... and my "lofty goal" would be half that, or 249 FPE.... If you are over 180 FPE (and well over 950 fps), you would get closer by using a heavier bullet, about 90 gr. should put you at (or over) 950 fps (which is where my loft goal is intended to be used).... That increases the bullet mass as a percentage of the total, and should push the FPE higher.... It would be interesting to see what you would get with a 100 gr. bullet, I would think 200 FPE is within reach....
Exceeding the 50% goal can be done by using a heavier bullet.... This is because it changes the ratio of bullet mass to total mass of bullet plus air.... Air at 3200 psi weighs about 64 grains per CI.... Your barrel, at that pressure, contains about 120 gr. of air.... So, at least in theory, it might take a 120 gr. bullet to get to 50% of the theoretical maximum.... This also explains why short barrels can help exceed the 50%.... They contain less mass of air, so the bullet becomes a larger percentage of the total mass.... I have said before that I should probably revise my lofty goal formula to take this into account.... but when nobody except Marco gets there, it seems kind of pointless.... Still, I may do that someday, just because.... ;)
IMO, you have done a great job on your build.... Congratulations.... 8)
Bob
Yes 36" long barrel.
My design pressure will be 3000psi. So about 466fpe is about the maximum energy I expect for this barrel. I'm confident I could hit your Lofty Goal of 50% by using a heavier projectile or a lower air pressure. But my velocity goal for the 70gr-73gr slugs is 1060fps. A Lofty Goal of 50% does not fit my design requirements.
The nice thing about working on a subsonic maximum FPE design, it's all (almost all) flow. We can ignore expansion and still come out with a fairly accurate result. Ignoring expansion simplifies the calculations considerably.
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Yep, I agree.... Your way of calculating Theoretical Maximum FPE (in the bullet) is much more realistic than Lloyd's calculation for absolute maximum FPE, which is what I use, which includes the FPE given to the air as well.... I agree that if bullet mass = air mass, then 50% of Lloyd's calculation should be the limit, except for one thing.... all of the air mass is not getting accelerated to the MV of the bullet.... Also, any of these estimates ignore other losses, such as bore friction, pressure drop in the reservoir, etc.etc.etc.... That is why I came up with my "lofty goal" of 50% of Lloyd's absolute maximum FPE.... However, as we have seen, with a heavy enough bullet (or a light enough air mass), it is possible to exceed that 50%.... which is why I should probably add a factor taking into account both the bullet mass and (part of) the air mass.... Right now, I'm too lazy, since only Marco has managed to get over 50%.... Although adding in those factors would allow it to be used on Helium.... hmmmmmmmmmmmm.... ::)
Bob
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Yep, I agree.... Your way of calculating Theoretical Maximum FPE (in the bullet) is much more realistic than Lloyd's calculation for absolute maximum FPE, which is what I use, which includes the FPE given to the air as well.... I agree that if bullet mass = air mass, then 50% of Lloyd's calculation should be the limit, except for one thing.... all of the air mass is not getting accelerated to the MV of the bullet.... Also, any of these estimates ignore other losses, such as bore friction, pressure drop in the reservoir, etc.etc.etc.... That is why I came up with my "lofty goal" of 50% of Lloyd's absolute maximum FPE.... However, as we have seen, with a heavy enough bullet (or a light enough air mass), it is possible to exceed that 50%.... which is why I should probably add a factor taking into account both the bullet mass and (part of) the air mass.... Right now, I'm too lazy, since only Marco has managed to get over 50%.... Although adding in those factors would allow it to be used on Helium.... hmmmmmmmmmmmm.... ::)
Bob
"...Lloyd's calculation for absolute maximum FPE..."
What is the formula for that?
For a maximum power from an airgun barrel, pellet friction is a nearly insignificant loss. Free flowing ports, valve with sufficient dwell, along with a sufficiently large plenum, and you can ignore pressure drop too. Those losses are a different problem related to the ports/valve/hammer/plenum. The Cothran valve leave almost nothing on the table. That leaves the barrel_volume x pressure as the determination of total FPE available for a given barrel.
"Lofty Goal" is the ratio of pellet_FPE/total_FPE. FPE is directly proportional to mass. So the Lofty Goal is the same ratio as pellet_mass/total_mass.
And since FPE is proportional to velocity squared, the Lofty Goal is related to the velocity squared ratio. I can derive the formula as it's fairly simple:
Lofty Goal = 1 - V^2/Vmax^2
And if you have a particular Lofty Goal in mind, you can calculate the velocity that determines it:
Velocity = Vmax x sqrt(1 - Lofty_Goal)
Vmax is the maximum speed of the gas in the barrel. You can use the speed of sound as the maximum, or you can calculate the maximum if you know the density of the air.
for 3000psi air, Vmax is 1366fps.
I like to set a velocity goal of 1060fps, that means that my Lofty Goal is predetermined:
1 - (1060 x 1060)/(1366 x 1366) = 40%
If instead, I had "chosen" a Lofty Goal of 50%, then my velocity would be:
1366 x sqrt(1 - 0.50) = 966fps
For various Lofty Goal values, the equations give this:
Lofty Goal, fps
90%, 432 fps
80%, 611 fps
70%, 748 fps
60%, 864 fps
50%, 966 fps
40%, 1060 fps
30%, 1143 fps
20%, 1222 fps
10%, 1296 fps
Those are not really goals, as that is what a barrel will always do. The "goal" becomes building a plenum/valve/hammer/port system that does not restrict to the point where they are not able to get close to those numbers.
I got somewhat close with my modified Marauder valve and electronic hammer, but the Cothran Valve does a job better and even at .25 caliber.
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FPE = Force x Distance = Bore (in)^2 x PI/4 x Pressure (psi) x Barrel Length (ft).... This assumes constant pressure (infinite reservoir volume) and NO losses.... It calculates the maximum possible FPE of the bullet plus the air mass ejected from the muzzle.... As you know, there are many losses.... the largest of which is due to accelerating the air mass, only the remainder can accelerate the bullet.... Then you deduct friction, and the pressure drop due to a finite reservoir (or plenum) volume.... I have built a lot of PCPs, and I have never managed to quite end up with 50% of the theoretical maximum FPE in the bullet, except in a few rare circumstances (where the bullet is relatively heavy, and the velocity is therefore under 900 fps).... Since I usually target 950 fps, I consider 50% of the theoretical maximum to be my "lofty goal".... Over the years, I have had a LOT of people ask me what they can expect from a PCP.... I give them my simple formula, and tell them that is a lofty goal, and if they achieve it, they are doing better than I have.... The only caveat is that the formula is intended to be used with air, and with a bullet weight that achieves about 950 fps (2 FPE per grain).... AFAIK, Marco is the only one to have bettered that (by using a short barrel at high pressure), although Doug Noble has come close, and exceeded it by using a bullet heavy enough that it is under 950 fps....
Are there alternate ways to calculate an FPE goal?.... Absolutely, but they have more variables, and including plenum volume, bullet weight, gas density, and barrel length to bore ratio.... If you should choose to develop your own goals, please don't let me stand in your way.... One of the problems is figuring out how much energy is lost in accelerating the gas, and to really know that, you must end up using some factor of how much mass to include, as not all of it reaches the MV of the bullet.... I'm trying to keep it simple for the average Joe.... and I use it all the time for my own projects, just to give me an idea what I can reasonably expect.... It will not be as precise if you have a very long barrel, a very heavy bullet, a very light bullet, or a very short barrel.... If you use Helium, it completely goes out the window, that 50% will end up being more like 70%....
If you use such a light projectile that you can reach 2000 fps, then the mass of the gas is FAR greater than that of the projectile, and you will be lucky to get to 5%.... As an example, my 6mm PCP, firing a 1.8 gr. airsoft BB at 2090 fps reached only 17.5 FPE, but with a 75 gr. lead bullet in the same gun, I got 1025 fps = 175 FPE.... The theoretical maximum FPE is 487 FPE, so one resulted in 36% efficiency, and the other in just 3.6%, from the same gun with the same tune.... The air mass in the barrel was about 115 gr., so using your formula my lofty goal was 39% for the bullet (which I almost achieved), and just 1.5% for the airsoft BB (which I more than doubled).... For the airsoft BB, obviously there is something wrong with the lofty goal estimate.... I would suggest that using all of the air mass just doesn't work in that case....
As I have said many times before there are better ways to do it.... but every one of them requires more input than barrel volume and pressure.... I like to apply the K*I*S*S principle, especially when just doing a simple estimate....
Bob
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...Since I usually target 950 fps, I consider 50% of the theoretical maximum to be my "lofty goal".... Over the years, I have had a LOT of people ask me what they can expect from a PCP.... I give them my simple formula, and tell them that is a lofty goal, and if they achieve it, they are doing better than I have.... The only caveat is that the formula is intended to be used with air, and with a bullet weight that achieves about 950 fps (2 FPE per grain).... AFAIK, Marco is the only one to have bettered that (by using a short barrel at high pressure), although Doug Noble has come close, and exceeded it by using a bullet heavy enough that it is under 950 fps....
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If you use such a light projectile that you can reach 2000 fps, then the mass of the gas is FAR greater than that of the projectile, and you will be lucky to get to 5%.... As an example, my 6mm PCP, firing a 1.8 gr. airsoft BB at 2090 fps reached only 17.5 FPE, but with a 75 gr. lead bullet in the same gun, I got 1025 fps = 175 FPE.... The theoretical maximum FPE is 487 FPE, so one resulted in 36% efficiency, and the other in just 3.6%, from the same gun with the same tune.... The air mass in the barrel was about 115 gr., so using your formula my lofty goal was 39% for the bullet (which I almost achieved), and just 1.5% for the airsoft BB (which I more than doubled).... For the airsoft BB, obviously there is something wrong with the lofty goal estimate.... I would suggest that using all of the air mass just doesn't work in that case....
...
Bob
If you have a 50% Lofty Goal, then 966 fps is the theoretical maximum air velocity. 950 fps is pretty close and such a small discrepancy could be accounted for if you have relatively small losses that a system such as this could have.
The "Lofty Goal" formulas can only work on a system that uses the maximum total barrel energy AND subsonic velocities. The Lofty Goal has no application when shooting at 2000fps. As soon as it becomes sonic, any additional acceleration comes from expansion of the gas. So even with an infinite plenum, pressure downstream in the barrel can be way below the plenum pressure. You can't verify it. For supersonic velocities, the barrel energy falls below the maximum that you calculated from the available pressure, so unless you do some complex calculations, there is no way of knowing what the total barrel energy is. For subsonic velocities (including all porting), barrel pressure is equal to plenum pressure, and that makes it simple.
Your 50% and 950fps is a realistic goal.
My 40% and 1060fps is a realistic goal.
50% and 1060fps is impossible.
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Your 50% and 950fps is a realistic goal.
My 40% and 1060fps is a realistic goal.
50% and 1060fps is impossible.
I would generally agree with that conclusion, for most typical PCPs.... but I'm pretty sure Marco won't.... ;) .... I don't know where his thread is where he posted the results that gave 60%, hopefully he will link to it.... as I think you may be surprised what can be done with a short barrel and high pressure (I certainly was!).... I did find some partial information in this thread, check out my calculations in Reply #87.... Unfortunately there are no pics any more.... :(
https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87 (https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87)
The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE....
The result of interest is 331 m/s (1086 fps) with 45.5 gr. @ 270 bar = 119 FPE = 60%
As I said in that thread from 2018, my "lofty goal" formula needs a tweak for situations where the air mass is small and/or the bullet mass is large.... ;) .... If I did the math right, in this case they are about equal.... :o
Bob
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No reliable photo hosting, all the pictures seem to vanish after some time. Most annoying. Need to see if I can find the pictures from my old phone.
Well the gun is not your average build, valve has been used to make 7-800fpe on .457, 11.5 or 12mm peek poppet radius seat on poppet 11mm port in to 10mm mirror finish transfer, all edges radius, barrel is hand lapped to a very long lead in, about 100-150mm, cant remember the correct value. But the bullet gets to move very easily.
Its about how fast you get the air behind the bullet not the flow until the bullet starts moving.
After that you want max flow all the way to the muzzle.
I don't care about air consumption, air is the most easiest consumable in this hobby.
I like racing and pushing the envelope.
Will be pushing it further again when spring comes, have bigger valve and double air capacity for the twenty at works.
Marko
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Your 50% and 950fps is a realistic goal.
My 40% and 1060fps is a realistic goal.
50% and 1060fps is impossible.
I would generally agree with that conclusion, for most typical PCPs.... but I'm pretty sure Marco won't.... ;) .... I don't know where his thread is where he posted the results that gave 60%, hopefully he will link to it.... as I think you may be surprised what can be done with a short barrel and high pressure (I certainly was!).... I did find some partial information in this thread, check out my calculations in Reply #87.... Unfortunately there are no pics any more.... :(
https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87 (https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87)
The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE....
The result of interest is 331 m/s (1086 fps) with 45.5 gr. @ 270 bar = 119 FPE = 60%
As I said in that thread from 2018, my "lofty goal" formula needs a tweak for situations where the air mass is small and/or the bullet mass is large.... ;) .... If I did the math right, in this case they are about equal.... :o
Bob
OK. Something does not compute. 197fpe - 119 fpe = 78fpe. That's not enough to accelerate 40gr of air to 1086fps. Maybe 30gr of air? Density can fall off as gas expands, but there is usually an accompanying pressure drop. Was this room temperature air? No way for me to verify that data (test temperature, pressure/velocity/etc.), but I need to look at my theories(assumptions?) as I think something is wrong with them.
Those "realsitic" % values that I was quoting might only apply to a specific barrel configuration (caliber/length/pressure).
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No reliable photo hosting, all the pictures seem to vanish after some time. Most annoying. Need to see if I can find the pictures from my old phone.
Well the gun is not your average build, valve has been used to make 7-800fpe on .457, 11.5 or 12mm peek poppet radius seat on poppet 11mm port in to 10mm mirror finish transfer, all edges radius, barrel is hand lapped to a very long lead in, about 100-150mm, cant remember the correct value. But the bullet gets to move very easily.
Its about how fast you get the air behind the bullet not the flow until the bullet starts moving.
After that you want max flow all the way to the muzzle.
I don't care about air consumption, air is the most easiest consumable in this hobby.
I like racing and pushing the envelope.
Will be pushing it further again when spring comes, have bigger valve and double air capacity for the twenty at works.
Marko
sign up for yahoo mail , its free and comes with flikr which is super easy to use and huge capacity... no ads either
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Is there an error here......
The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE
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Is there an error here......
The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE
The math is correct. When things don't seem to match up, the data needs to be verified. For instance, a likely place for error would be the pressure measurement. It's possible that the pressure was actually higher than that, but if we did not know that, than all the resulting values could be as shown, even if they are not physically possible.
Then again, it's possible that the data is all correct, and there is something missing from our models that make the formulas unrealistic.
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https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87 (https://www.gatewaytoairguns.org/GTA/index.php?topic=144971.87)
The theoretical maximum FPE for a .223 cal. 15.5" barrel at 270 bar (3915 psi) = 3915 x (.223 x .223 x PI/4) x (15.5 / 12) = 153 lbf. x 1.29 ft. = 197 FPE....
The result of interest is 331 m/s (1086 fps) with 45.5 gr. @ 270 bar = 119 FPE = 60%
As I said in that thread from 2018, my "lofty goal" formula needs a tweak for situations where the air mass is small and/or the bullet mass is large.... ;) .... If I did the math right, in this case they are about equal.... :o
Bob
Bob, I looked at the numbers for quite awhile and can't find anything wrong with the way that I come up with maximums. Even with no losses, I can't get those results from the data shown.
15.5" x .223 barrel at 3916fpe, Maximum barrel 197fpe - so far so good
sending a 45.5gr pellet at 1086fps - I can't find the "free energy" to make that work on paper.
I can't verify the data, and unless I see the "magic" in the valving. I'll assume that there were data errors in that test. Instrumentation, calibration or reading problems are a likely culprit (chronograph, pressure gauge, pellet scale, air temp, etc.)
I'm sticking with what I know.
This is the maximum possible that I get for the 15.5", .223 barrel, 3916psi that was indicated:
45.5gr pellet at 965fps, Lofty Goal 47.7%
and that is assuming no losses, so in reality, they will be a little below this.
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I think it's quite simple, Scott.... The entire 45 gr. of air does not get accelerated to the muzzle velocity of the bullet....
The density of air at 270 bar is 297.5 kg/m^3 = 75.2 gr./in^3.... That works out to 45.5 gr. of air, if the barrel (0.605 CI) is full of 270 bar air.... When the bullet exits the muzzle, some of the air has just left the valve and is barely moving, so the average velocity of the air is not 1086 fps.... That is exactly why a formula based on the weight of the bullet plus the assumed weight of the air is doomed to failure, IMO.... As you know, Lloyd's internal ballistics spreadsheet uses only half the mass of air released by the valve in each time increment.... It produces a pretty good model of what is happening inside a PCP.... Interestingly, it works well for Helium as well, if you use the density of He instead of air.... My guess is that is why....
Use half the mass of air in the barrel, plus the mass of the bullet, travelling at 1086 fps.... If half that 45.5 gr. air mass is accelerated to 1086 fps that works out to 59.6 FPE, plus 119 for the bullet, a total of 178 FPE.... which is 90% of the maximum theoretical 197 FPE.... Certainly no laws of physics broken there.... ;)
I simply don't believe that the entire air mass ends up travelling 1086 fps.... Do you see any reason that must be the case?.... Marco's numbers pretty much prove otherwise, don't you think?....
Bob
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I think it's quite simple, Scott.... The entire 45 gr. of air does not get accelerated to the muzzle velocity of the bullet....
...
I simply don't believe that the entire air mass ends up travelling 1086 fps.... Do you see any reason that must be the case?.... Marco's numbers pretty much prove otherwise, don't you think?....
Bob
No, I don't see any reason why not, and if Marco's data is good, then also yes.
Bob, I like your simple model that uses full pressure and full air density for the entire barrel length (pressure x barrel volume). And it seems to match closely with what I'm getting in actual tests. But if I go back to my much more complex spreadsheet model, I get different (higher performance) predictions. The spreadsheet model allows adiabatic expansion to occur simultaneously with flow. So there is a gradient in the air density. So I don't have all air at full velocity. I have never been able to match the performance of that model with an actual test of my own. It seems too good to be true that it is possible to match the full theoretical spreadsheet model. If I could meet my spreadsheet's prediction, I'd be at 216fpe, not the 175 fpe that I'm currently getting in my tests. That would be great. It seems counterintuitive that we can effectively utilize some of the expansion energy while also going for maximum power. Though that has always worked in a spreadsheet, I now want to try it in real life.
Look at the three pictures at the bottom of this post. I run the following numbers (based on Marco's input data) through my spreadsheet and I show the results. It's exactly what Marco gets in his tests. 1st picture is part of the data input screen. 2nd picture is the numerical integration based on 1cm barrel increments. I show it out to 39cm. The 3rd picture show the velocity and fpe calculations out to 16".
Okay Marco, I'm going to research your old posts and see if I can tweak my design to use some of your recommendations.
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Its interesting to see the theory and calculations that I never do.
I just build something and test it how it works. And if I post some results it's something that I have repeatedly done.
The porting idea came from Lloyds maximum velocity test, when he used the pellet stationed in the breech with cams and full reservoir pressure behind it.
BIG valve and ports to feed the barrel should give similar results.
Well it works.
How does the models take in to account barrel friction and possible lubrication?
We use silicone to lube the pellets.
And just a fun fact from using petroleum based lapping compound, it will ignite when accumulating in to the barrel. Air gets heated high enough when the valve opens. Have witnessed muzzle flash from a pcp when lapping.
Marko
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...
The porting idea came from Lloyds maximum velocity test, when he used the pellet stationed in the breech with cams and full reservoir pressure behind it.
BIG valve and ports to feed the barrel should give similar results.
Well it works.
How does the models take in to account barrel friction and possible lubrication?
We use silicone to lube the pellets.
...
Marko
The simple model that rsterne uses for Lofty Goal calculations and I was trying to use for my subsonic gun, treats the gas as in-compressible. It's more like a hydraulic model rather than a pneumatic model. It could never work for supersonic velocities. And apparently not great for all subsonic instances. I wrote the more complex spreadsheet a few years ago as a way to model the supersonic tests that LLoyd was doing. It gave results that closely matched Lloyd's test data. But it did not work all that well for other real world builds, at least not until your tests. So there might be some feature in common between yours and Lloyd's dump gun that is not present on most conventional valve guns. That's what I'd like to discover.
As for accounting for lubrication, I do have an input for coefficient of friction. And that value is buried somewhere in the calculations, where? I can't remember. The Coef F value can be between 0 and 1. I have been using 0.1 which works good for yours and LLoyd's. I can get the spreadsheet to match some of my other tests but only when I use a significantly higher value. I need to use a value of 0.8 to make this .257 barrel calculations match the test results. 0.8 seems too high to be realistic. And even when at 1.0, some test data for other barrels still does not match.
You said you used a tapered bore on the barrel. Is it a rifled barrel?
Do you have an in-line valve? A conventional valve usually bends the air path 180 degrees between throat and barrel. Maybe that's a problem as I have not accounted for it in any way in my spreadsheet.
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John and I were starting to build a larger kiln to handle larger investment castings. After doing some research, we ended up getting a large 1980's pottery/ceramics kiln in great condition, at a good price. I had to make a 500 mile trip to pick it up but I decided I rather do that than spend time building one. John plans on making a digital controller for it to replace the old style electro/mechanical controller.
I'm already using the best of the three aluminum breeches, but this new kiln should allow for even better large casting results. I'm replacing some more of the PLA parts with investments castings. Pictured below are the PLA and aluminum versions of the bottle bracket and a series of replaceable transfer port slides. It only takes minute to swap ports via one screw. The ports are 0.250", 0.210", 0.170", and 0.140" diameter. There was a fifth port at 0.125" dia, but the casting did not turn out well enough to use. I'm not sure if I would ever use one that small anyway. Besides than changing regulator pressure, changing the transfer port seems to be a good way to tune a Cothran Powerhouse valve for various velocities. And swapping ports seems more repeatable. I plan on polishing the 0.250" port just to see if it helps.
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This is a dedicated benchrest gun, so weight is not much of a concern. Here is the gun with a 2000cc bottle.
EBR has only allowed 580cc bottle for the latch few years, so if they continue that, I'll use my small bottle. But they allow filling during the match, so you can only guess why they put a limit on bottle size. A new benchrest league is allowing tethering so there is also that option. I prefer to have a bottle that can finish a match without refilling or tethering. So I'll do that when it's allowed.
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looks awesome , people are gonna freak out when you show up with that to a bench rest competition.
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Yes rifled barrel, can't remember the twist, maybe 8"
Conventional porting, valve seat almost at the bend.
Good looking setup you have!
I just missed a furnace from one auction. Would be fun to cast some of the not so critical parts.
Marko
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Yes rifled barrel, can't remember the twist, maybe 8"
Conventional porting, valve seat almost at the bend.
Good looking setup you have!
I just missed a furnace from one auction. Would be fun to cast some of the not so critical parts.
Marko
A valve seat almost at the 180 degree bend is typical. Conventional porting and rifled barrel. Nothing special there. I'll try sizing projectiles and lubing them. That might get me a little closer.
We have not had good results casting valve bodies or anything that needs to hold high pressure over time. Most other aluminum parts seem good for vacuum investment casting.
For non-critical parts, no need to cast. PLA goes soft at relatively low temperatures, and it's biodegradable, so it might break down over time. Outside of that, it's very stiff and has properties comparable to engineering thermoplastics. It works good for non-critical parts. I have some PLA parts on my guns that have been there for nearly three years. I might replace some of them with aluminum as time goes on.
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Yes nothing special just flow efficiently rounded everything and big.
Short side radius slightly D ported. Works in engines so why not in guns.
No plastic for me, only hand grip or butstock other that that its steel or aluminum. Don't like plastic, makes the part feel like a toy. But that's just me.
Marko
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I'll be going to a fixed 2200psi regulator as I think it will be more consistent. I know that some of these little cheap gauges on guns and regulators are not all that accurate. I compared them to a higher quality regulator gauge today and found variation of +/-10%. I did some more velocity testing today and calibrated with the better gauge.
34gr JSB .25, 226cc unregulated fill
(start 1600psi)
1097 fps
1071
1026
1010
994
950
928
907
888
851
825
(end 720 psi)
73gr 257420 slugs
2200 psi - 973fps, 153fpe
1450 psi - 837fps, 114fpe
1200 psi - 787fps, 100fpe
The 973fps is probably a good velocity for the 257420 slug, so I think 2200psi will work good for those. I have not decided exactly how I'm going to handle the 34gr pellets, either a smaller transfer port or a different bottle with a 1200psi output. I just ordered some parts to build a regulator tester so I can fine tune them better. Also a bigger gauge for the gun that is hopefully more accurate. I currently use a vent on the gun to drain the plenum/airtube when I want to swap bottles. I ordered another vent that will go between the tank and plenum that will allow me to swap bottle without the need to drain the plenum.
For rsterne, some Lofty Goal numbers:
.257, 36" long, 73gr
Calculated numbers:
2200psi - 342.4fpe in barrel, 156.6fpe in slug, 45.7%
1450psi - 225.7fpe in barrel, 126.6fpe in slug, 55.3%
1200psi - 186.7fpe in barrel, 113.4fpe in slug, 60.7%
Test data:
2200psi - 153fpe/342.4fpe = 44.7%
1450psi - 114fpe/225.7fpe = 50.5%
1200psi - 100fpe/186.7fpe = 53.6%
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Pretty interesting confirmation that when the slug is significantly heavier than the air charge, you can exceed 50%.... Exactly why I tell people my 50% lofty goal is intended for a slug doing about 950 fps.... and is invalid if the velocity is significantly lower than that.... eg. using a slug that is way below have the FPE in weight.... Your example at 1200 psi has the slug at 73% of the FPE attained....
The one I still don't fully understand is Marco achieving over 60% while the slug equalled the weight of the air, and achieving 1086 fps.... It must have something to do with the combination of high pressure and a short barrel.... ???
Bob
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... I tell people my 50% lofty goal is intended for a slug doing about 950 fps.... and is invalid if the velocity is significantly lower than that....
Bob
did you mean to say:
... I tell people my 50% lofty goal is intended for a slug doing about less than 950 fps.... and is invalid if the velocity is significantly lower higher than that....
Test data:
2200psi - 153fpe/342.4fpe = 44.7% @973fps
1450psi - 114fpe/225.7fpe = 50.5% @837fps
1200psi - 100fpe/186.7fpe = 53.6% @787fps
Lower velocity requires less pressure, so the air is less dense making the projectile proportionally heavier. Reducing the barrel length would also make the projectile proportionally heavier than the air.
I still have not figured out Marco's, but I did get over 50% (50.5%@837fps, and 53.6%@787fps).
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No, I meant what I said.... If the bullet is heavier (or the pressure less) it will travel slower, and can exceed the 50% lofty goal because it is a greater percentage of the total mass (bullet plus air).... It is a LOFTY GOAL, ie not something easily acheived.... I have never hit it with a slug going 950 fps, I usually get to between 90-95% of the goal (ie 45-47% of the maximum FPE) with my best builds.... I call it a "lofty goal" for a reason.... it is HARD to achieve....
You are not the first person to exceed my 50% lofty goal by using a heavy bullet at less than 950 fps.... Tim (shorty) did it with a modded MRod, shooting a pellet at under 600 fps on low pressure.... and Doug Noble has done it with a Condor, shooting a 90-100 gr. bullet in the low 900's in a .257 on "normal" pressures of 2800-3600 psi.... I have done it more than once, with heavy (for caliber and pressure) slugs, shooting in the high 800's.... AFAIK, Marco is the only person to exceed my "lofty goal" and simultaneously exceed 950 fps....
Remember, my "lofty goal" is intended to be simple, understandable for anyone, and easy to calculate.... It is simply 50% of the maximum FPE a PCP can generate (which is force times distance).... It works 99% of the time, which is good enough for me.... If it didn't, I would add a factor for the air mass.... Would that be better?.... Yeah.... Is it necessary?.... Not in my opinion, because all it is, is a way for guys to understand what they might expect to see from a certain barrel volume and pressure, if the gun is maxed out.... ;)
Bob
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.... It is a LOFTY GOAL, ie not something easily acheived.... I have never hit it with a slug going 950 fps, I usually get to between 90-95% of the goal (ie 45-47% of the maximum FPE) with my best builds.... I call it a "lofty goal" for a reason.... it is HARD to achieve....
OK. Now i get what the lofty goal is. It's 50% at 950fps. Yes, 50% will be difficult to achieve at 950fps, and generally easier at lower velocities.
Maybe any desired velocity should have its own lofty goal? >50% for lower velocities? <50% for higher velocities.
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Go for it!.... I always build with a 950 fps target (for many reasons), so I'm quite happy with what I have.... and most guys seem to appreciate the simplicity of it.... ;)
By the time a PCP gets tuned down to an acceptable level of efficiency, they are more like 40% or less, anyways.... ::) .... By way of example, my .257 Hayabusa has a 28" barrel.... At 3000 psi, my "lofty goal" was 181 FPE, and I achieved (wide open) about 162 FPE (90% of the goal, or 45% of the theoretical max).... I detuned it to shoot at 133 FPE in order to get a decent bell curve and shot count.... that is only 37% of the maximum.... ;)
Another example is my .257 Condor, with Doug's valve and hammer spring.... It has a 26" barrel, and is filled to 3600 psi, which gives a lofty goal of 202 FPE.... I achieved 193 FPE with a 92.6 gr. bullet at 969 fps. which is 95.5% of my goal (47.8% of the maximum).... Even with a 113 gr. bullet at 883 fps, I could not get over 196 FPE (48.5% of maximum).... Detuned for a 7-shot bell curve, with an efficiency of 1.15 FPE/CI, it shoots at 176 FPE (43% of maximum).... If I tether it, I can tune it up a bit, to 187 FPE (46% of maximum) and still get over 1 FPE/CI.... 8)
I plotted velocity and FPE vs. bullet/pellet weight, and got the following for the Condor.... Shots are at maximum power, tethered at 3600 psi....
(https://hosting.photobucket.com/albums/oo221/rsterne/257%20Condor/.highres/257%20Condor%20Dougs%20Vel%20FPEjpg_zps4xp1hlsn.jpg) (https://app.photobucket.com/u/rsterne/a/47e225fe-debc-45b3-b424-216ee17f5a07/p/f749d5a3-4aee-492b-b86f-712a10c1adf4)
Below 37 gr. are pellets, and they are all supersonic, as are the two lightest slugs.... Note how the FPE is plateauing at over 100 gr.... just below my "lofty goal".... ???
Bob
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Scott, I have a question for you.... In Reply #297, you posted the following:
73gr 257420 slugs
2200 psi - 973fps, 153fpe
1450 psi - 837fps, 114fpe
1200 psi - 787fps, 100fpe
The numbers above that (for a 34 gr. pellet), stated 226 cc reservoir, unregulated.... Was that the same for the above?.... Answer = NO!.... If you started at 2200 psi, and shot 3 shots as above, for the first 2 shots it looks like you used 1000 psi, is that correct? (you don't give a pressure after the 3rd shot).... If that is the case, you produced (153 + 114) = 267 FPE from (1000 / 14.5) x (226 / 16.4) = 70 x 13.8 = 950 CI of air used (at STP).... That works out to 0.28 FPE/CI, which to me says that the valve is still open after the bullet leaves the muzzle.... Would that be a correct assessment?.... Incidently, would that not mean you used (950 x 0.30) = 285 gr. of air to produce those 2 shots?....
Bob
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Scott....how’s the lofty goal of putting a hole in paper where it should?
Mike
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Scott, I have a question for you.... In Reply #297, you posted the following:
73gr 257420 slugs
2200 psi - 973fps, 153fpe
1450 psi - 837fps, 114fpe
1200 psi - 787fps, 100fpe
The numbers above that (for a 34 gr. pellet), stated 226 cc reservoir, unregulated.... Was that the same for the above?.... If you started at 2200 psi, and shot 3 shots as above, for the first 2 shots it looks like you used 1000 psi, is that correct? (you don't give a pressure after the 3rd shot).... If that is the case, you produced (153 + 114) = 267 FPE from (1000 / 14.5) x (226 / 16.4) = 70 x 13.8 = 950 CI of air used (at STP).... That works out to 0.28 FPE/CI, which to me says that the valve is still open after the bullet leaves the muzzle.... Would that be a correct assessment?....
Bob
The 34gr was a shot string after charging the plenum once. You can use that to calculate air use efficiency.
I don’t have enough 73gr slugs yet to waste on a shot string. The three 73gr shots involved draining/filling the plenum to a calibrated/measured pressure each time, and taking one shot at that setting. I already had data for the 73gr at higher pressures. That was a prelim to when I install a 2200psi regulator.
Air efficiency with the Cothran valve has been in the .7 range. I’m not too worried since I have a 2000cc tank that I can mount to the gun.
I can reduce energy by reducing pressure or by reducing the transfer port. Reducing pressure raises the lofty goal and increases efficiency some. Reducing the port size lowers the lofty goal but raises the air efficiency more.
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Scott....how’s the lofty goal of putting a hole in paper where it should?
Mike
Not a lot yet with this .25/.257 barrel. Here is one test from Feb 22. It was windy. Hard to even get a good zero at 50yds. 10 shots, 50yds, 34gr JSB@1090fps. There seems to substantial aerodynamic jump maybe? Hoping a lower velocity will help.
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Ya...that’s pretty speedy. I was shooting the 25.4 monsters last fall at 1000ish...but have found out there was no advantage over 910-930.
I’m guessing 10 mph variance in high/low wind velocity there. That’s a good group for holding constant.
Mike
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There is a National 50 match at Joes in Oxnard on the 14th. You should come down. I’m going to be there to deliver a couple guns. It should be fun.
Mike
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Ya...that’s pretty speedy. I was shooting the 25.4 monsters last fall at 1000ish...but have found out there was no advantage over 910-930.
I’m guessing 10 mph variance in high/low wind velocity there. That’s a good group for holding constant.
Mike
900-1000fps is where I'll likely end up for both 34gr pellets and 73gr slugs. I'm narrowing down the minimum pressures I will need for those velocities when running full bore ports. Looking like 800psi-1200psi range for the pellets and 2000psi-2500psi range for the slugs.
The current plan is to have two bottles for the gun. Easily to swap. One smaller/lower pressure bottle for the pellets (450cc or 580cc) and one larger higher pressure bottle for the slugs (2000cc).
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There is a National 50 match at Joes in Oxnard on the 14th. You should come down. I’m going to be there to deliver a couple guns. It should be fun.
Mike
I might do that. Do you have any JSB .25 King Heavy 33.95gr (not the MKII)? I don't have enough left for a match and Pyramyd is out of stock.
The JSB MKII pellets that I have does not do as well.
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Scott, thanks for the info on how the data was collected for the 73 gr. slugs.... I realize I was barking up the wrong tree, there.... ::)
Bob
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I have a case of these.
Mike
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I have a case of these.
Mike
Those are the MKII. I need the other kind.
I just checked my schedule. I'll be at the Sonoran AAFTA GP that weekend. I do plan on shooting at Joe's again, but not March 14th.
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Some more things of interest today.
I weighed the 2000cc bottle and reg empty and then immediately after a 300bar fill from the compressor.
3.62 lb. before
4.98 lb. after
-------
1.36 lb.
My calculations show 2000cc of air at 300bar should be 1.6 lb.. The heated air from the compressor could account for the lower mass.
The last part of the transfer port is a 90 degree curve/sweep as printed/cast. A little rough. With the new 2200psi reg (actually outputting about 2100psi), I got 928fps average with the 73gr slug. I smoothed out the port with my Dremel type tool and then averaged 942fps. There might be a little more to be had in that area.
The input gauge on the new regulator reads about right when in the middle of the range (3000psi), but read 1500psi as 500psi, and 5500psi at 4500psi. So it reads way low at the bottom end and way high at the top end. These cheap gauges can be off by 20%. Don't rely on them unless calibrated to a known gauge.
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At 300 bar and 20*C, air density is 323 kg/m^3.... You can't use Boyle's Law at 300 bar because of the VanDerWaals effect....
https://www.peacesoftware.de/einigewerte/luft_e.html (https://www.peacesoftware.de/einigewerte/luft_e.html)
2000 cc is 0.002 m^3, so that air should weigh 0.646 kg = 1.42 lbs.... If your air was at 30*C (86*F), the density at 300 bar would be 311 kg/m^3 and your weight of air would be 1.37 lbs.... ;)
Bob
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At 300 bar and 20*C, air density is 323 kg/m^3.... You can't use Boyle's Law at 300 bar because of the VanDerWaals effect....
https://www.peacesoftware.de/einigewerte/luft_e.html (https://www.peacesoftware.de/einigewerte/luft_e.html)
2000 cc is 0.002 m^3, so that air should weigh 0.646 kg = 1.42 lbs.... If your air was at 30*C (86*F), the density at 300 bar would be 311 kg/m^3 and your weight of air would be 1.37 lbs.... ;)
Bob
You are correct and I did not take that into account. Air is not a perfect gas and becomes less elastic at higher pressures. It gets worse fast when you get over 3000psi. Diminishing returns over that. At very high pressures, it takes ~10x pressure increase to get a ~2x density increase. At 12,000psi, air is about as dense as water.
I installed a lower pressure paintball regulator for next Monday testing at 50yds. 34gr@880fps. That's 59fpe at ~800psi.
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The .22 HP has turned into a .25/.257 HP.
I want to get better precision on my testing and measurements. I've now got a Labradar and will take it to my next outdoor shooting session. I also wanted to get better measurement of pressure. I made a regulator tester with a 2-1/2" gauge, and set each of my regulators close to what they should be. Two of them were good and two of them needed some shimming. I also replaced the small regulator gauges with 1-1/2" gauges so I could better monitor any pressure changes.
800psi regulator
800-900psi output @ 1000-4000psi input (stock)
1200psi regulator
1150-1250psi output at 2000-4000psi input (stock)
1800psi regulator
1750-1850psi output at 2000-4000psi input (2x .009 shims)
2200psi regulator
2100-2200psi output at 2500-4000psi input (2x .009,+ 1x .002 shim)
I cast a bunch of 70-71gr slugs with my new Arsenal mold. 980fps@2200psi (150fpe). I can get 180fpe but the higher pressure regulators are not all that consistent yet, shot count drops fast, and I probably don't need to go any faster than 980fps with these slugs.
The 34gr pellets are 1034fps@1200psi with full ports.
port size, fps
0.25, 1034fps
0.21, 1000fps
0.17, 910fps
The breech is getting better with each casting attempt. My smaller printer is slower but is setup with a smaller nozzle for higher resolution. I'm currently printing the next breech pattern on it.
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For fun, I made some PLA slugs and pellets. The slugs were a fit tight and the pellets were a little loose. I took two shots with each.
2200psi
8.1gr slugs
1668fps (50fpe)
1651fps (49fpe)
2.8gr pellets
1760fps (19fpe)
1748fps (19fpe)
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ahhahahaa nice.. supersonic pla
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Pretty amazing how the FPE drops when the majority of the mass is the air, isn't it?.... ::)
Bob
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Pretty amazing how the FPE drops when the majority of the mass is the air, isn't it?.... ::)
Bob
Until you calculate the air mass. The total kinetic energy (fpe) is mostly there with most of it in the air molecules, and the remainder in the much lower mass projectile.
It does make one realize why you get quickly diminishing returns when you get past the mid 900's fps. Most of the potential doesn't end up in the projectile.
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Yep, one of the primary reasons I tune in the mid 900's (the other being less wind drift).... In addition, the huge drag increase above 1000 fps means than not only do you waste air to get there, the slug loses a lot of that hard earned velocity and energy in the first few yards.... Pretty much 3 strikes and you're out in the Transonic region.... ::)
Bob
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I got a chance to get to the range today with my new Labradar and newly cast Arsenal 257420 slugs. I took 50 shots with the unsorted slugs. I had some consistency issues in these first batches but I am getting better with the casting process. I wanted a good baseline in this trip and I got that. The first three shots were not picked up by the Labradar so I went into the menu and changed the sensitivity from 5 down to 1. It picked up every shot after that. But I only got 21 recorded before the battery warnings started. The Labrader uses up the AA batteries quickly. I have an 8000mah rechargeable/solar lithium pack coming in but now I suspect that I might want something larger for longer sessions.
(http://www.scotthull.us/Armada/Armada-range-00.jpg)
(http://www.scotthull.us/Armada/Armada-range-01.jpg)
Some of the slugs were a not 100% filled and were unsorted, so that could have affected consistency/accuracy/BC values a little. Left example had poor fill. right example was good:
(http://www.scotthull.us/Armada/Armada-range-03.jpg)
The Labradar worked well as I figured it out. I used the Labradar iphone app to control/arm it remotely so that was convenient. I had it set to record velocities at muzzle, 10yd, 25yd, 50yd, 75yd, and 100yd. It picked up all 21/21 shots at 10yd, 25yd and 50yd. It got flaky past 50yds. Some gave 0 and some were obviously wrong. It got maybe 14/21 good readings at 75 yds, and maybe 9/21 at 100yds.
The data file show the first three shots as 34gr but that was before I input the correct 70.5gr for projectile mass. If I throw out the fastest and slowest shots, I get 19 shots averaging 952fps, with an SD of 6.75fps. The BC was disappointing as the few shots that were the best were only 0.110, and some were under 0.07. But I still have not cut a barrel lead-in and slugs were forced in with some shaving in the process. I will do the lead-in now that I have my slug mold. Maybe it will be a little better after that.
Labradar Data file downloaded from sim card:
(http://www.scotthull.us/Armada/Armada-Labradar-00.jpg)
I'm trying to use better gauges these days to get better pressure readings. The regulator is set to 2100-2200psi into a 225cc plenum. I'm finding that charging the bottle past 4000psi does not seem to get me as many extra shots as expected. So I charged the 2000cc bottle to 3540psi and after 50 shots was at 2990psi. Using the Sikes airgun calculator, I get 1.53 FPE/cu-in per shot. That seems high for a 140+fpe airgun, but it does have a 36" barrel and I'm testing in the optimal pressure ranges. My spread sheet shows that I should get about 194 shots at 142fpe on a full 4300psi. That agrees closely with the sikes calculator.
I was not all that careful on accuracy. I shot two groups with most of the shots within a 2moa circle at 100 meters. It was windy:
(http://www.scotthull.us/Armada/Armada-range-02.jpg)
Results are:
I'm happy with the Labradar. ++
I'm not happy with the BC of the 257420 slugs so far (BC=0.11). --
I'm surprised at the efficiency and high shot count (easily 100+ shots@140+fpe). +++
I'm OK with the initial accuracy (2moa @100m). +
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I don't know what range you used to calculate the BC from the LabRadar data, but the 100 yd. data is very poor, and even the 75 yd. data has some questionable velocities.... As you said, maybe only 2/3rd of the 75 yd. data usable.... What do you get for the BC if you average the MV and the 50 yd. data (throwing out questionable data from shots 9 & 16)?....
The VanDerWaals effect will not give you the extra shot count above 4000 psi that you would expect using Boyle's Law.... The higher you go above 3000 psi, the fewer extra shots you get for each 100 psi....
Bob
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I don't know what range you used to calculate the BC from the LabRadar data, but the 100 yd. data is very poor, and even the 75 yd. data has some questionable velocities.... As you said, maybe only 2/3rd of the 75 yd. data usable.... What do you get for the BC if you average the MV and the 50 yd. data (throwing out questionable data from shots 9 & 16)?....
The VanDerWaals effect will not give you the extra shot count above 4000 psi that you would expect using Boyle's Law.... The higher you go above 3000 psi, the fewer extra shots you get for each 100 psi....
Bob
I used the best performers to calculate the 0.11 BC (shot #17 for instance). I'll see if I can add BC calcs to the spreadsheet so I don't need to manually calculate each. But I know it would be way less than 0.11 for this string. The Labradar manual says the estimates for maximum range are:
.223 (5.56mm), 40-60yds
.308 (7.72mm), 80-100yds
.355 (9mm), 100-130yds
My guess is that the .257 with a .22 diameter base would be close to the .223 ability to register. And the reading out to 50yds all look good. I'd say that all the readings that I highlighted in green were good. Those highlighted in yellow might be questionable but potentially usable, and those highlighted in red look wrong since they don't follow a logical trend-line:
(http://www.scotthull.us/Armada/Armada-Labradar-01.jpg)
That VanDerWaals effect made me rethink the need to fill any of my tanks to 4500psi, and now maybe even keep under 4000psi.
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The difference in fill out on those slugs looks like the difference between a pressure pour and a regular pour.
Not sure what method you used or if you may have been experimenting to see what works best.
Your castings are looking really nice. What temp do you use to burnout the pla?
Dave
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The difference in fill out on those slugs looks like the difference between a pressure pour and a regular pour.
or not letting the sprue cool long enough, or the lead not hot enough, or the mold not hot enough, or the sprue plate not hot enough....
I still get a few like that, notably the first couple of pours when the mold is coming up to temp (and yes, I use a hot-plate to preheat it).... I count to 5 after the sprue pool solidifies before cutting the sprue, to set a regular rythym.... If I am still seeing bases like that, I increase the heat of the melt....
HINT: Bottom pour pots like the 10 lb. Lee can have the spout MUCH colder than the melt, which means the first cavity you fill can look like that, even when everything SHOULD be working OK.... I lift the handle to "squirt" out a bit of lead before filling the first cavity on each pour to eliminate that problem.... You end up with a pile of lead pretty quickly, which I just push off to the side to add back into the melt along with the sprues and any cast-off bullets when the pot is getting low.... Obviously do this carefully, to avoid splashing yourself with molten lead....
Bob
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I use the basic Lee 90021 pot that is rated for 4 pounds of metal and a Lee ladle. I originally ordered a 4 cavity mold as I suspected that 5 cavity would be at the limit of what the ladle can easily handle. I switched the order to 5 cavity as I can always upgrade the pot and ladle at a later time. I run the pot at about the 8.5 setting. I preheat the aluminum mold by setting it across the pot opening. I hold the mold handle and tip it slightly down. I dip the ladle. A full pot makes it easier to get a full charge in the ladle. I move the ladle down above the mold as I pour attempting to fill equally and fully. If I overfill the first cavities too much, I run low by the 5th cavity. The 5th cavity is the one that gets the most fill errors. Even the 4th once in awhile. and sometimes the early cavities if I move over them too fast. When I concentrate on the work and get into a rhythm, they all come out of the mold fully formed. A good portion of the lead ends up as a continuous sprue cap. I dump that on the work bench after swinging the sprue cutter. After I get several sprue caps on the bench, I use needle nose pliers and sink them back in the pot.
https://leeprecision.com/lead-ladle.html
https://leeprecision.com/precision-melter.html
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... What temp do you use to burnout the pla?
My casting buddy informed me that the investment plaster is cured for 4 hours at 1400 F as recommended by plaster mfg. The PLA burns out during that process. Not sure at what point the PLA is completely eliminated.
Besides PLA, he has done burn out of resin (photo-polymer) printed patterns, and it takes the full 4 hours.
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Thanks for that info Scott. Much appreciated. My little kiln can handle that without issue. (Outside, I would have to guess it smokes quite a bit)
Dave
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I question the 50 yard data on shots 9 & 16 in particular, they are way too low to fit with the trend of the others, IMO....whereas the 25 yd. data for those two shots is OK.... The rest I would just average the MV and 50 yd. velocity and use the averages to calculate the BC.... BTW, don't fall for the "simple" BC calculations on some of the airgun websites.... Use ChairGun (G1), Strelok (G1), or the BC (G1) calculator on the JBM website.... Any time you find a "simple equation" to calculate the BC it undoubtedly uses a constant drag model (usually Cd = 0.20 or 0.22) and they do NOT work in the Transonic (they ignore the huge drag increase there).... You have to calculate the actual Cd for your projectile at your average Mach number, using the delta distance and delta velocity, and the mass and cross sectional area of your slug (complex in itself, and watch your units), and then correct for your local atmospheric conditions.... Then divide that into the Cd of the G1 model for your average Mach number.... and then multiply by the SD to get the BC (G1)....
Bob
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I reran the BC data for some of the shots using the ChairGun G1 and it does not look as bad as I had originally thought. The individual trend lines of shots 9 and 16 look valid, but the BC is low when compared to the others. I finally cut a lead-in on the barrel and will retest later to see if I get more consistency. And after that, test at different muzzle velocities.
I also did a very light polish on the inside of the barrel and then pushed some slugs through. Not bad, but It looks like it might benefit from a heavier polish.
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Scott- Of all of my TJ's barrels, for some reason the 2 that I've had in .257 1:14 have been the roughest I have seen. Don't be afraid to get aggressive with it. I made a lead lap, then fire lapped, then polished with JB's and Mother's my most recent one and it is still so tight it prefers .256 slugs. After all of that the bore still shows inclusions when viewed with a borescope, but engraving on slugs is like a mirror... My .300, .357, and .457 TJ's all cleaned up much better than I could get my 25-20 liners.....
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Scott- Of all of my TJ's barrels, for some reason the 2 that I've had in .257 1:14 have been the roughest I have seen. Don't be afraid to get aggressive with it. I made a lead lap, then fire lapped, then polished with JB's and Mother's my most recent one and it is still so tight it prefers .256 slugs. After all of that the bore still shows inclusions when viewed with a borescope, but engraving on slugs is like a mirror... My .300, .357, and .457 TJ's all cleaned up much better than I could get my 25-20 liners.....
I remember reading that in your posts. I'll shoot it this way first. It is a little tight. The bore is a go with a 0.249" pin gauge, and no-go with a 0.250" pin. The slug dia measures 0.2555"-0.2565" before pushing/sizing. After a push through, slug shows a max of 0.2555". I'd like to eliminate any burrs on the bore and groove. The dimensions show that there is a little meat that I can remove from the lands and still be in tolerance. And when I decide to get more aggressive, I'll take it slow. Too much lead-in or crowning can be fixed, but too much lapping and of the bore, well - you just live with it or replace the barrel. Fortunately, the barrel is easy to remove, so I won't mind lapping/testing in small stages.
Note: First, I'll check my lead-in and crown as closely as possible to make sure the burrs are not from there.
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I like that 2000cc bottle, how much does it weight? Those bullets look like the BT version of 257420, in my gun they group best at slightly lower velocity (920ish fps). We measured them at 0.17-0.18 BC with Timo's labradar.
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I like that 2000cc bottle, how much does it weight? Those bullets look like the BT version of 257420, in my gun they group best at slightly lower velocity (920ish fps). We measured them at 0.17-0.18 BC with Timo's labradar.
The bottle weighs 3.3 lbs. empty. With a regulator/valve installed and 3000psi of air, it weighs 4.8 lbs.
My Arsenal slug mold is the boat tail version of the 257420. In my first tests at 950fps, I got 0.152 as the best BC. I plan on testing it next with the adjustable regulator at various velocities. Probably from 900-1020fps. With the latest capacitor discharge circuit, the single 4700uf capacitor is limiting me to about 2500psi with voltage maxed out (63v). If I run the Cothran valve too close to the edge, velocities get inconsistent. Running at 2300psi-2400psi gives me about 1020fps (160fpe) and a little leeway on the hammer strike.
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I've made over a dozen breeches for this project. Only 5 or 6 actually got tested. The first two that I tested were plastic and they actually worked well enough. The last three were cast aluminum. It was a progression with many design changes early on. The last several have had no design changes. The only differences in those last three cast breeches was the casting quality. This last aluminum breech could be better cosmetically, but it filled out out fairly well so I decided to paint it flat black and call it done.
This breech is very specific to the Benjamin Armada. There is no cocking mechanism as the gun has an electronic hammer. The current design is ambidextrous (swap out left or right projectile shuttle). Integrated 20moa, 2.5" high, 34mm scope mounts. Barrels is clamped in place and is quick/easy to swap by via four socket head screws. Barrel prep is easy as there are no ports in the barrel.
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Just WOW .... Always thinking outside the box.