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All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: mackeral5 on March 03, 2021, 07:21:43 PM

Title: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 03, 2021, 07:21:43 PM
I am considering adding a regulator to my .257 that is the subject of this thread:

https://www.gatewaytoairguns.org/GTA/index.php?topic=181490.80 (https://www.gatewaytoairguns.org/GTA/index.php?topic=181490.80)

Normally I would just start testing, but rather than just going into a process of investing a bunch of lead and nitrogen I thought I would see if I could get some help here in making some calculations, to directionally see if it is a worthwhile venture.

I have the parts to assemble a 160cc regulated plenum and 340cc HPA storage tube.  The 340cc storage is rated for up to 3600psi. 

Let's just assume I can get the gun to perform 160fpe around 2500psi reg setpoint.  And just to be safe let's assume a low efficiency of 1.0:1.  I am pretty sure I can tune for significantly better than that, but let's at least have a realistic starting point. 

How many shots should I be able to get on a 3600psi fill?  If the number is 10 or more, it's a no-brainer for me to proceed.  If it is 10 or less, I won't be quite as interested but may still convert to regulated.

Thank you in advance for your insight.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: Scotchmo on March 03, 2021, 09:02:41 PM
You should get 10 shots, maybe 11 or 12 with the last two falling off the reg.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 04, 2021, 12:52:37 AM
You have 340 cc of air, and 1100 psi of headroom (fill pressure minus setpoint).... If you get 160 FPE, at 1.0 FPE/CI, you will be using 160 CI per shot.... You have available (340 / 16.4) x (1100 / 14.5) = 20.7 CI x 75.9 bar = 1570 CI of air available.... As Scott says, that should, in theory, net you (1570 / 160) = 10 shots, if you can get an efficiency of 1.0 FPE/CI at your 160 FPE goal.... If you can do that and tune on the knee, so that the velocity ticks up a few fps when you hit the setpoint, you could get a couple more by shooting below the setpoint by ~200 psi.... If you can get higher efficiency, your shot count would increase....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 04, 2021, 10:01:51 AM
Thanks for the responses and thank you for your patience in sharing the formula for the 10000 time. 

I am going to add it to my spreadsheet this time. 
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 06, 2021, 09:46:10 AM
Just a quick update.  I set the Huma right at the 170 bar mark.  The tune is currently around 150-155fpe.  I am low on nitrogen so further testing will have to wait for later in the week.  Air consumption seems to be in alignment with what is described above. 

So far I really like shooting this long barreled .257 under regulation.  it is very different from shooting a 34gr pellet shooter at 100 yards. 

More to come next week. 
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 17, 2021, 07:08:24 PM
I ended up frustrated with the regulated tube/tune and swapped back to unregulated. 

It was very difficult to creep up on HST without bouncing the hammer off the valve nut, and an accompanying loss of velocity. 

As a sidenote, with a few other changes to the pin probe and leade, it will now send 72gr 1030fps at a miserly 2600psi.

At some point I will make another poppet with a slightly longer stem and revisit the regulated tube/tune. 

I also wonder how long a Huma takes to refresh and stabilize a 160cc plenum, this could be contributing to my challenges--I may not be waiting long enough between shots.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 17, 2021, 10:29:55 PM
Can you turn a pin into the front of the hammer, slightly less in diameter than the valve stem?.... or insert such a pin into the front of the hammer?.... That should allow you to push the valve stem just past flush with the back of the valve.... Maybe?....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 18, 2021, 05:41:34 AM
Can you turn a pin into the front of the hammer, slightly less in diameter than the valve stem?.... or insert such a pin into the front of the hammer?.... That should allow you to push the valve stem just past flush with the back of the valve.... Maybe?....

Bob

Great suggestions, but for my capabilities it will be more practical to just make another poppet.  Finding the 2600psi/just under 170fpe was enough encouragement to reengage. 

I have one in process.  To think I used to make these with a cordless drill and dremel, lol...  I know it isn't a lathe/mill, but this old $150 Craftsman drill press from the 70's has already paid for itself.  I am no machinist nor is any of this perfectly machined, my techniques are probably 100% wrong.  But the poppet seals, flows and the designs have proven to be durable......

(https://i.imgur.com/havStoK.jpg)


The poppet lower in the pic is my original peek poppet that has seen well over 5000 firing cycles probably closer to 10k....  The valve is equipped with a Cobra chamber, hence the oring.  The lower poppet is the new unit in process, just needs the oring groove cut and stem cut to length. 

Valve throat is .375, as the BD is built as a .357.  For .257 I am experimenting with choking the throat a bit.  With the .375 throat, throat-stem area is .0951.  Bore-probe area is .0459.  I think this contributes to low flow velocity across the seat, and I "think" this makes the closing cycle less controllable.  By adding the .250 step it chokes the throat minus stem area down to .0614,  I "think" this will help with the closing cycle by increasing air velocity across the seat.  If it hurts things it can simply be turned off.  Having 2x throat area is new territory for me....this is just a working theory, I have no facts/science to back it up.

(https://i.imgur.com/ceNUMP8.jpg)
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 18, 2021, 07:23:53 AM
I finished the poppet and set stem protrusion to .300 vs .22 of my original poppet.  Bear in mind the .22 protrusion works fine for high pressure, max fpe unregulated tunes.  Once trying to regulate down in the 2500-2600psi range it just didn't give enough valve lift (beyond the "curtain"= dwell) prior to bouncing the hammer off the valve nut.... 

Now i have a rough tune of 10 shots averaging 1005fps with 68.8gr hollowpoints from the MP .257-640 mold  Not quite the 160fpe I was targeting, but not too far from it.  If the tune proves stable I will reassemble and put some rounds on paper. 

The Huma seems to refresh the 160cc plenum fine, so long as you wait 40 seconds or so between shots. ES was less than 15 across the 10 shots.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 18, 2021, 01:14:51 PM
I run a .357 cal valve in a .224 with no issues, I just use a tapered transfer port.... Tunability remains fine.... Large throat and poppet doesn't seem to bother it one bit.... Mind you, it's a balanced valve, not a Cobra type....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 18, 2021, 03:44:05 PM
I run a .357 cal valve in a .224 with no issues, I just use a tapered transfer port.... Tunability remains fine.... Large throat and poppet doesn't seem to bother it one bit.... Mind you, it's a balanced valve, not a Cobra type....

Bob

I think I am doing 2 things wrong---1)  expecting too much 2)  running too high on the curve for a given regulator set point.

it seems to require much more air to generate 160+fpe on 160cc of plenum/340cc res vs a 500cc unregulated tube. 

I may do some regulated testing without the Cobra chamber just to see what if any effect it has. 

Resolving the short stem protrusion issue has been helpful, that eliminated some noise from the process...
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 18, 2021, 07:20:27 PM
Quote
it seems to require much more air to generate 160+fpe on 160cc of plenum/340cc res vs a 500cc unregulated tube.

That is not surprising, you are getting about 3 times the pressure drop during the shot, all else being equal.... The average pressure has to be less.... The 1 cc per FPE for a plenum is not a guarantee you will equal the power with a full size reservoir.... It is just the point at which adding volume doesn't really buy much, you can get there easier by increasing the setpoint by 100 psi or so.... Decreasing the plenum below that size, however, loses power quickly, and needs larger increases in setpoint to get back performance.... and eventually you lose efficiency and the ability to get back to the power you want (low powered tunes excepted, of course)....

If you want 160 FPE, use a setpoint pressure that will allow you to hit 170-175 FPE wide open, and then back the velocity down 3-5% from the plateau to get the efficiency back.... That pressure would likely give you even more than 175 FPE with the full reservoir volume and unregulated....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 18, 2021, 09:21:45 PM
Thank you for sharing your thoughts Bob. 

The Huma is pretty much maxed out around 2600 psi or so, which makes sense as they are advertised with a 170bar max.  The adjustment screw will go further, but I am uncertain as to if it is doing anything when turned beyond the 175bar mark.

At this regulator pressure the plateau seems to be at 1030fps with my 68gr slugs.  When dialing down to 970fps or so it will get 14-15 shots on a 3500psi fill. 

I think this is a good place to stop chrony testing and put some rounds on paper.  I would have shot some targets this evening but the wind has been blowing pretty good
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 18, 2021, 10:09:07 PM
That would seem to be excellent efficiency.... Your HP reservoir is 340 cc, correct?....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 19, 2021, 08:15:26 AM
That would seem to be excellent efficiency.... Your HP reservoir is 340 cc, correct?....

Bob

Correct, 340cc hpa side, 160 plenum.  I have not run it through Lloyd's calculator. 

I cannot put to words how frustrating the short stem protrusion was----I couldn't find the plateau and when I got close to it strange things happened.  Funny thing about bouncing the hammer off the valve, somehow it uses a ton of air this happens.   Anyway I am glad that challenge is out of the way and on to the next one.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 19, 2021, 01:03:30 PM
Here is what I get for efficiency, assuming you get 14 shots before it drops below the 2600 psi setpoint....

(3500-2600) = 900 psi / 14.5 = 62 bar.... (340 cc / 16.4) = 20.7 CI x 62= 1285 std. CI....

68 gr. @ 970 fps = 142 FPE x 14 shots = 1988 total FPE....

1988 / 1285 = 1.55 FPE/CI.... That seems pretty high, but that's what the numbers say.... If the last shot or 2 are below the setpoint pressure, then it would be less, because not only is the finishing pressure lower than 2600, but you are also using air from the 160 cc plenum once below the setpoint....

When the hammer bounces off the valve, it is probably then bouncing off the SSG or spring and reopening the valve.... just a guess.... Out of curiousity, what was the stem protrusion, compared to the throat diameter?....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 19, 2021, 01:30:20 PM
bob--  Thanks for the calculations.  I guess I should add that to my spreadsheet at some point.  It is going off reg so I'm sure air usage is a little higher. but that's still pretty good. 

My previous issue was trying to run up on the plateau.  it had awesome ES, but burned a bit more air.  In hindsight I allowed the noise of the short stem protrusion to create too much of a mental fog, lol....

Previously, stem protrusion was .220 on a .375 throat.   Now it is .300.   But, in order for this to be meaningful data I'll need to include some additional measurements, which I don't currently have available.  The hammer has a protrusion that goes into the valve nut.  This protrusion measures roughly .250.  I need to measure the depth of the valve retaining nut, which next time I'm in there I will. Unfortunately that requires full disassembly of the stock, due to the BD design....I cannot remove the hammer without removing an indexing/locating screw, and that screw cannot be accessed without splitting the stocks...IMO this is the only negative aspect of the BD design....

Here is a hammer, an OEM hammer with peek button.  It weighs 103grams.  Currently the gun is running an 80gram hammer. 

(https://i.imgur.com/hWY3LJI.jpg)

I neglected to state that I reinstalled the Cobra chamber.  It has been a while since I did any real Cobra tuning, and never at the upper energy ranges of a given application.  Normally I am using a small vent to help generate a short, snappy blast of air.   Thus I size the vents around 1/4-1/3 of the diameter of the chamber.  Ultimately I enlarged the vent from .100 to .120, this seems to help harmonize things a bit.  This one is a little over 1/3 chamber ID of .330 ID...

 
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 19, 2021, 02:08:48 PM
Huma seems to be pretty stable.  This batch of slug weighs in the 69.3-4 range averaging 965fps 

Refresh rate was more than adequate after removing the set screw restrictor (I forgot it was in there.)  I only waited long enough to reload, aim, shoot.  Max 30-40 seconds between shots.

15 shots, a full fill at 50 yards.

(https://i.imgur.com/9z8B5kn.jpg)

The group could have been smaller, but I couldn't tell if I was hitting the target for  several shots, so became a bit more sloppy in my aim.

Now move out to 102 yards.  Lower target was for sighting, upper target was 5 shot groups. 

(https://i.imgur.com/urETyqR.jpg)

I think this thread has come run its course, I'll move back over to the gun's thread in the big bore forum. 

Thank you for your contributions.

Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 19, 2021, 02:58:03 PM
If the last 2 shots drop the pressure to 2400 psi, the additional air used would be....

(200 / 14.5) x (500 / 16.4) = 13.8 bar x 30.5 CI = 421 std. CI.... Add that to the 1285 used above the setpoint and you get 1706.... and the efficiency drops to (1988 / 1706) = 1.17 FPE/CI.... which is still pretty decent for 160 FPE in a .257....  8)

I am very surprised that 0.220" of travel on a 0.275" throat (80%) was not enough to find a good tune.... Most of the time I only allow for valve stem travel of 2/3 of the throat diameter and never find the hammer hitting the back of the valve.... Efficient tunes often occur when the valve lift is only about 1/4 of the diameter, and never in my experience more than 1/2 the diameter....

Having a lighter hammer than OEM, you will need more spring energy to get the FPE you want.... and it will be accompanied by more lift to get the same dwell.... Opening the valve more than 1/4 of it's seat diameter doesn't increase the flow rate, so all gains in power must be made through dwell.... The dynamics of the lift to dwell are governed by the hammer mass, so a heavier hammer would give you the same dwell with less lift.... Perhaps that is the reason your hammer is hitting the back of the valve.... I would try the stock hammer again....

For an unbalanced valve (and the Cobra uses an air spring, it is not a balanced valve), my rule of thumb for hammers is the weight in grams times the travel in inches gives the FPE you can reasonably expect the gun to generate.... My unregulated .257 Hayabusa, running on 3000 psi with a conventional valve, used a 113 gr. hammer with 1.20" of travel (113 x 1.20) = 136 FPE.... It peaked at 160 FPE, and delivered a good, efficient tune of 135 FPE, just about where you are at.... I would get 12 shots within a 4% ES from 2960 psi down to 2280 on a 28 CI reservoir, for an efficiency of 1.13 FPE/CI.... It used bore-size porting, but did have a 0.088" bolt probe, which dropped the smallest port equivalent down to 0.241"....

With a balanced valve in the same gun, I am now using a 77 gr. hammer with 1.09" of travel reduced by an SSG gap of 0.150" at my current tune, so the actual (powered) hammer travel is only 0.94".... Multiplying those together only give (77 x 0.94) = 72 FPE (half the hammer strike), and yet the gun still delivers 136 FPE and with better efficiency at 1.30 FPE/CI... and with a lighter hammer spring to boot....  8)

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 19, 2021, 03:29:12 PM
If the last 2 shots drop the pressure to 2400 psi, the additional air used would be....

(200 / 14.5) x (500 / 16.4) = 13.8 bar x 30.5 CI = 421 std. CI.... Add that to the 1285 used above the setpoint and you get 1706.... and the efficiency drops to (1988 / 1706) = 1.17 FPE/CI.... which is still pretty decent for 160 FPE in a .257....  8)

I am very surprised that 0.220" of travel on a 0.275" throat (80%) was not enough to find a good tune.... Most of the time I only allow for valve stem travel of 2/3 of the throat diameter and never find the hammer hitting the back of the valve.... Efficient tunes often occur when the valve lift is only about 1/4 of the diameter, and never in my experience more than 1/2 the diameter....

Having a lighter hammer than OEM, you will need more spring energy to get the FPE you want.... and it will be accompanied by more lift to get the same dwell.... Opening the valve more than 1/4 of it's seat diameter doesn't increase the flow rate, so all gains in power must be made through dwell.... The dynamics of the lift to dwell are governed by the hammer mass, so a heavier hammer would give you the same dwell with less lift.... Perhaps that is the reason your hammer is hitting the back of the valve.... I would try the stock hammer again....

For an unbalanced valve (and the Cobra uses an air spring, it is not a balanced valve), my rule of thumb for hammers is the weight in grams times the travel in inches gives the FPE you can reasonably expect the gun to generate.... My unregulated .257 Hayabusa, running on 3000 psi with a conventional valve, used a 113 gr. hammer with 1.20" of travel (113 x 1.20) = 136 FPE.... It peaked at 160 FPE, and delivered a good, efficient tune of 135 FPE, just about where you are at.... I would get 12 shots within a 4% ES from 2960 psi down to 2280 on a 28 CI reservoir, for an efficiency of 1.13 FPE/CI.... It used bore-size porting, but did have a 0.088" bolt probe, which dropped the smallest port equivalent down to 0.241"....

With a balanced valve in the same gun, I am now using a 77 gr. hammer with 1.09" of travel reduced by an SSG gap of 0.150" at my current tune, so the actual (powered) hammer travel is only 0.94".... Multiplying those together only give (77 x 0.94) = 72 FPE (half the hammer strike), and yet the gun still delivers 136 FPE and with better efficiency at 1.30 FPE/CI... and with a lighter hammer spring to boot....  8)

Bob

Bob---  Throat is .375, not .275...  I've tested both hammers on both poppets, with the .220 protrusion both hammers bounced off the valve. Perhaps I wasn't very clear in my description and picture, but I attempted to explain with this particular style of hammer and valve mounting stem protrusion isn't the only measurement.  I need to measure and share the thickness of the valve nut to really understand how much lift is being achieved.  I apologize for not being more clear.

The .220 protrusion poppet only became an issue with higher dwell tunes.  Previously I have used that same poppet for over 340fp unregulated  and for a 15 shot tune of 160fpe in .357, with only 340cc of TOTAL air for both of these, again using the .220 protrusion poppet (same 29" barrel, just different tubes and hammer/spring systems.)  Stem diameter is .140, exhaust/transfer is .328, BTW..  This chokes down  to a .200x .300 oblong barrel port in the .257 barrel.

Only once I started trying out these .257 tunes did I run into challenges...

I typically run hammer with weights in grams that equal roughly FPE divided by 2-3, sometimes 4, depending on energy level.  Normally they are in free-flight, with exception to this gun and 2 others.  This applies to energy levels from 30 -600ish fpe....

IMO, with the Cobra valve, you want a light, fast moving hammer.  Achieve as much lift as possible prior to the pressure dropping outside of the chamber and the rapid closing cycle begins...perhaps I am interpreting data  and describing it incorrectly, but that is my best description of Cobra tuning. 

Mike
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 19, 2021, 03:58:32 PM
Sorry, I misread.... 0.220" is of course only 59% of 0.375", but still greater than the lift that you should need.... I guess if I understand you properly, even though the valve stem protrusion is 0.220", the hammer when sitting against the stem is less than that distance from the "valve nut".... How far can the hammer open the valve before it hits the valve nut?....

How light a hammer you can run depends on the travel you have available, in relationship to the FPE the gun develops.... and of course a balanced valve can use a much lighter hammer.... Running really light hammers is, IMO, problematic when striving for high power.... as they require too much (wasted) lift in order to get the required dwell.... It works fine at low to medium power, but you run into the kinds of problem you are facing when you push the FPE.... YMMV of course....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 19, 2021, 05:33:28 PM
During next teardown, which could be tomorrow, next week, or next month, lol..  I will take measurements on stem protrusion, hammer travel, etc. 

One of the coolest aspects of this hobby is there are many ways to skin a cat.  The data you and others freely share allows each of us to develop our own styles for setting up our guns.  There are many "wrong" ways and there are many "right" ways.  I do have a tendency to choose a less than conventional route at times...

IMO, the problems I am facing (and I use the word "problem" very loosely here as many would be satisfied here and simply call it "done") are primarily related to throat area and seat diameter being far disproportionate to bore area.  I'm not having any problem making power.  At 3500 psi it is breaking 240fpe and doing so not quite running wide open and with a fairly high friction bullet.  I predict this gun will break 250fpe with better ammo than the "lovern" style slug used for those numbers...   Marco's guidance around building a big powerplant and topping it with a small bore are  ringing very true here.   Due to the style of the BD valve and my limited fabrication abilities I don't have an easy way of making a new seat/throat....but perhaps at some point I will figure out a series of operations that I can execute on. 

Anyway, good stuff here and thank you for continuing the dialogue.

Mike
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 19, 2021, 07:08:39 PM
On the subject of light hammers...  For a very efficient 160fpe regulated tune (.357 88gr @ 915fps).  This skeletonized hammer will open the same valve used in the gun that is the subject of this thread, doing so in free-flight with average cocking effort.  But it does so at 120-125bar and with only about 80-90cc of plenum. 

(https://i.imgur.com/Skc9p03.jpg)
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 19, 2021, 09:57:18 PM
Mike, 240 FPE with a 29" barrel in .257 at 3500 psi is VERY impressive.... The "lofty goal" is only 219 FPE, so you are beating that by a fair margin.... I don't think even Doug Noble, with his highly modified Condors, has made those kind of numbers, even shooting a heavy bullet....  :o

Whoops, I see the barrel is 35.5" long, so that bumps the "lofty goal" to 268 FPE.... Still the 245 FPE you reported in the other thread is 91% of that, which is VERY impressive at nearly Mach 1.... I'm thinking that with a 120 gr. bullet in the high 900s you could easily top 250 FPE.... Congrats for sure....  8)

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 19, 2021, 11:51:28 PM
Mike, 240 FPE with a 29" barrel in .257 at 3500 psi is VERY impressive.... The "lofty goal" is only 219 FPE, so you are beating that by a fair margin.... I don't think even Doug Noble, with his highly modified Condors, has made those kind of numbers, even shooting a heavy bullet....  :o

Whoops, I see the barrel is 35.5" long, so that bumps the "lofty goal" to 268 FPE.... Still the 245 FPE you reported in the other thread is 91% of that, which is VERY impressive at nearly Mach 1.... I'm thinking that with a 120 gr. bullet in the high 900s you could easily top 250 FPE.... Congrats for sure....  8)

Bob

Bob...I know it is confusing with my discussing different calibers, barrel lengths, etc and the same gun.. My .357 barrel is only 29".  The .257 is 35.5".  I am very close to ordering 35" of .357 from TJ's, for this gun. 

I enjoy testing different hammer weights, spring combos, etc.  This pic shows a range of different hammers, weights, springs for the Bulldog platform.  The largest hammer weight, which is 16.5grams, along with the OEM hammer is what I used for the 245fpe shots.  The SSG is what I use with the skeletonized hammer for the 160fpe regulated .357 tune.  The SSG is equipped with a Wilson Combat 24# 1911 recoil spring. 

I appreciate the congratulations and kind words.  I believe the Bulldog is a very capable 180 degree valve platform, but at the end of the day it's not going to keep up with Doug's inline guns....It is still fun demonstrating a platform's capabilities in mostly uncharted territory.

Mike
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 20, 2021, 01:31:52 AM
My Hayabusa project has been through many variations.... The Mk. I was a regulated .22 and .25 cal pellet shooter.... The Mk. II started life as a .224 cal unregulated, shooting the 41.3 gr. RWS slugs from Holland, and then was later fitted with a .257 cal barrel on the same action.... I made up a second receiver for it for .308 and .357 cal LW barrels, again unregulated.... All these used a probe to load the pellet or slug.... The Mk. III version increased the reservoir volume and pressure to 3600 psi, and was fitted with a .410 shotgun barrel in its' own (very long) receiver, and a .457 cal rifle barrel.... It was a beast to cock (nearly 40 lbs.) with a hammer over 8 oz. with a 2" travel, and hit 550 FPE.... I then built a 7mm on the Mk. II tube, but with a retracting bolt.... Next I did a balanced valve for the .410 / .457, which finally made it OK to cock.... but that was the early "SS" valve and suffers from stiction, and I have yet to change it over to the new valve....

The last iteration was when I was developing the "simplified balanced valve", and it was built for the .357 cal Mk. II, but I then worked my way down in caliber, through .308, 7mm, .257 all the way to .224 cal, without changing the valve, only tapering the transfer ports to blend from the large exhaust port down to whatever I needed for the smaller caliber barrels.... and fitting with progressively lighter hammers.... This is when I found that was a good way to go, similar to what you are doing with your Bulldog going down to .257 cal.... It has been quite the round trip!....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 20, 2021, 10:03:23 AM
I just realized that I neglected to include the pic of bulldog hammer stuff....

(https://i.imgur.com/BdJh3qK.jpg)

I followed your Hayabusa project over the years.  That is where I gained the insight to finally convert a Cothran to a HST tuneable state.  Your Hayabusa threads, Disco Double threads, Tale of 3 Brods are threads I often revisit as reference material.  I do not have the capabilities to fabricate anywhere near what you do, but I emulate as much as I can in my builds.  Your sleeving of barrels with CF, Add Scott's ultralight hammer, Cobra valve development by Scott and Travis, then the SSG, add in minimal sealing margin peek poppets and reduced stem diameters-- those are the foundations of all of my builds...

The 8oz of hammer and 2" of travel...  I guess I could experiment with some heavier, slower moving hammers.  The most experience I have in that area was when I first received an early WAR Flex...  It was unregulated and had the heavy steel hammer.  When you pulled the trigger it went "kerrplunkk."  Now it did have a decent unregulated shot string and was pretty easy to cock.  I just couldn't take the long lock time and sound, so it quickly was converted to a regulated, light hammer, Cobra valve setup....

I think the oversized throat concept likely works very well with your balanced valves, largely due to the manipulated closing cycle.  I think in an unbalanced valve without such a controlled closing cycle the oversized throat decreases velocity across the seat and allows the poppet to essentially float/dwell off the seat longer.  Again, I am not a scientist and I may be misinterpreting data.  Your early recommendations of sizing throat area to roughly 10% greater than the rest of the porting has worked very well for me in being able to generate decent power and efficiency at the same time, with unbalanced valves. 

Mike
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 20, 2021, 03:18:10 PM
I know that the 10% oversize throat works well in an unbalanced valve.... Going larger doesn't seem to buy anything, however.... You could be right about the oversized valve working better when balanced.... but on the other hand I have never seen any INCREASE in power or efficiency from doing it, just no losses.... I think this is one case of the theory involved in the pressure drop with the larger than caliber port volume being unimportant.... While the pressure drop undoubtedly occurs, getting rid of the restrictions where the flow turns the corners in a "proper" sized port by making them oversize seems to compensate for any theoretical loss....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 20, 2021, 04:59:41 PM
Something I have always wondered about was closing force, as in the closing force that can be increased/decreased with stem diameter. 

for example, say in this .375 throated, unbalanced valve that currently has a .140 stem.  If I increased stem to .176  how would that effect the closing cycle?  or more extreme, say to .200 stem diameter, or even .250 stem diameter? 

I picked .176 as I already have a valve with the stem passage increased to that size, the one I use with my Cothran conversions.  So I wouldn't be risking any hard parts becoming paperweights.  I would just be out the time/materials involved in making the poppet.  The other sizes would potentially consume a valve..

Your thoughts?
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on March 20, 2021, 06:52:12 PM
I was JUST emailing with Mike Niksch of Thomas BR Rifles about this today!.... He has tried two widely varying stem diameters, and told me there is NO doubt that the larger stem closes faster, and requires significantly more hammer strike for the same dwell and FPE....  This is directly in line with theory, where the largest closing force (while the valve is open) is the stem area times the pressure in the throat during the shot (basically operating pressure).... Mike says this is a consistent and repeatable phenomenon....  8)

So, using a larger valve stem may decease the power (ie flow) if the throat is small, but would not likely do that if the throat is really big.... However, you will likely need more hammer strike to overcome the 58% increased closing force on the larger stem, which should reduce the dwell and FPE significantly....  ;)

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on March 20, 2021, 10:03:45 PM
Interesting info on stem diameter. 

I have another reason to "go in" anyway, so over upcoming days I will make up a .176 stemmed poppet and report back.  Later next week I will see how the larger stem effects my .357 tunes as well. 

I do have these weird visions of a .200 stem, .250 throat valve for a very efficient unregulated pellet shooter...  I don't believe a traditional 2 piece poppet could be made to last though....  Perhaps a Hatsan style valve would have to be used?
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 06, 2021, 06:25:28 PM
A bit of an update here.  I did make a .176 stemmed poppet but didn't see a measurable difference in power nor efficiency. 

I have reverted back to some unregulated testing.  Specifically, I reduced valve throat to .270 by epoxing a piece of .375 x .250 6061 tubing in the valve throat.   Then I made a  a .140 stemmed peek poppet.  Poppet seal is a little over .300.  Poppet is designed to run the OEM Bulldog return spring, old school PCP tuning here.  Early results are promising with regards to producing a flatter unregulated string.  As I often find myself with these builds, I am running low on nitrogen so 3000psi fills are all I have to work with right now.  I am hopeful to achieve a reasonably flat string starting at 3600psi, using Arsenal 85gr, which is a mold ordered in early March.  Per USPS tracking the mold should arrive tomorrow.....If the .270 throat/.140 stem combo doesn't move enough air I will drop down to a 2mm stem and see how that does. 

A pic of the poppet and reduced valve throat/seat.  I had my doubts about pulling this one off, but it still seals after 100 or so rounds across the chronograph....  The valve opens easy enough now that I can use an SSG with the hammer in freeflight, this has not been possible with the OEM .375 throat at pressures above 2000psi or so.

Disregard my Sharpie I use as lay up dye....brake clean takes it right off.

(https://i.imgur.com/99c8crg.jpg)
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on April 07, 2021, 02:43:43 AM
Following. Theory says you need that 2mm stem to flow enough air for barrel size porting, it will be interesting to see how/if it holds up. If it works I may copy it for my Evanix, less hammer spring pressure on sear makes for a better trigger feel. Are there any commercial manufacturers using 2mm stems?
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 07, 2021, 07:58:52 AM
My old Edgun R3 is the first gun I ever saw with a 2mm stem.  But it was regulated, typically  at 150 bar or less.   The edgun throat was only .250 or so. 

After my experience with the Edgun, 2mm stems became the norm for my builds, but again they were mostly regulated and relatively smallish valve throats.
I do have a 2mm stem in one unregulated 3kpsi fill gun, a 70fpe .25, again a smaller valve throat.

If I do try a 2mm stem on this gun, it will be pushing one harder than I ever have, in both pressure and throat area.  There is definitely potential of failure.  At least the Bulldog has a bleed screw incase I drive the stem through the poppet to the point of no stem protrusion, lol...

I am hopeful that the long barrel helps with the less than bore area porting.  It will be late next week before I can exchange my nitrogen cylinder, so no full fill testing until then.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 07, 2021, 09:26:24 AM
A quick note about current energy levels.  Shooting a 70gr slug, at 2900psi it maxes out at 1003fps.  This is with the .270 throat/.140 stem and .200 exhaust, 35.5" barrel.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on April 07, 2021, 09:30:46 AM
My old Edgun R3 is the first gun I ever saw with a 2mm stem.  But it was regulated, typically  at 150 bar or less.   The edgun throat was only .250 or so. 

After my experience with the Edgun, 2mm stems became the norm for my builds, but again they were mostly regulated and relatively smallish valve throats.
I do have a 2mm stem in one unregulated 3kpsi fill gun, a 70fpe .25, again a smaller valve throat.

If I do try a 2mm stem on this gun, it will be pushing one harder than I ever have, in both pressure and throat area.  There is definitely potential of failure.  At least the Bulldog has a bleed screw incase I drive the stem through the poppet to the point of no stem protrusion, lol...

I am hopeful that the long barrel helps with the less than bore area porting.  It will be late next week before I can exchange my nitrogen cylinder, so no full fill testing until then.

Using PEEK poppet would be a good idea. Alternatively metal poppet and PET-P or delrin seat.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 07, 2021, 10:15:11 AM
My old Edgun R3 is the first gun I ever saw with a 2mm stem.  But it was regulated, typically  at 150 bar or less.   The edgun throat was only .250 or so. 

After my experience with the Edgun, 2mm stems became the norm for my builds, but again they were mostly regulated and relatively smallish valve throats.
I do have a 2mm stem in one unregulated 3kpsi fill gun, a 70fpe .25, again a smaller valve throat.

If I do try a 2mm stem on this gun, it will be pushing one harder than I ever have, in both pressure and throat area.  There is definitely potential of failure.  At least the Bulldog has a bleed screw incase I drive the stem through the poppet to the point of no stem protrusion, lol...

I am hopeful that the long barrel helps with the less than bore area porting.  It will be late next week before I can exchange my nitrogen cylinder, so no full fill testing until then.

Using PEEK poppet would be a good idea. Alternatively metal poppet and PET-P or delrin seat.

Agreed on peek, I only use peek when making my poppets.  The only exception is when I replace Cothran valve seals with delrin.   Believe it or not, for my limited fabrication capabilities peek is easier for me to use....
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 09, 2021, 07:34:16 AM
The 85gr Arsenal mold arrived.  They are actually dropping closer to 87gr.  On 2900psi and the choked down porting (.270 throat/.140 stem) max velocity is 900fps, but very wastful in doing so.  While this porting works pretty well for bullets in the 68-72gr range, it is not going to work for the heavier bullets. 

Going to take a break from .257 testing for a bit and focus some time on replenishing my ammo supply.  I may make up a 2mm stemmed poppet if only to more thoroughly test before abandoning the small valve throat concept for this application.

If one were building a .30 or smaller pellet shooter on the BD platform this method of reducing valve throat would be very helpful.  Perhaps even a .22 , .177, or .172 slug shooter.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on April 09, 2021, 08:43:10 AM
Do try the 2mm stem, I'd really like to hear the results.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 09, 2021, 02:58:22 PM
Do try the 2mm stem, I'd really like to hear the results.

Will do, over the next week or so.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 22, 2021, 09:08:06 PM
Do try the 2mm stem, I'd really like to hear the results.

The 2mm stem has around 150 or so rounds through it, so far it is holding up. 
 
Putting things into perspective--with the 2mm stem and .270 throat at 3500 psi it maxes out around 1055fps with the Arsenal 257388 87gr .  The hammer is in .250" of FREE FLIGHT, zero preload!

Generally speaking, I believe a 2mm stemmed peek poppet is good for valves under .300" seat at pressures up to 3500psi.  Assuming no more than .300 unsupported stem protrusion, must be a straight line hammer vs hinged swinging hammer, etc.

Still testing various things.  Will get back to the unregulated Arsenal 257388 testing soon.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on April 23, 2021, 01:31:14 AM
Do try the 2mm stem, I'd really like to hear the results.

The 2mm stem has around 150 or so rounds through it, so far it is holding up. 
 
Putting things into perspective--with the 2mm stem and .270 throat at 3500 psi it maxes out around 1055fps with the Arsenal 257388 87gr .  The hammer is in .250" of FREE FLIGHT, zero preload!

Generally speaking, I believe a 2mm stemmed peek poppet is good for valves under .300" seat at pressures up to 3500psi.  Assuming no more than .300 unsupported stem protrusion, must be a straight line hammer vs hinged swinging hammer, etc.

Still testing various things.  Will get back to the unregulated Arsenal 257388 testing soon.

That sound extremely good! I would love to use a free flight hammer in my .257 and still being able to achieve 160 fpe. Reduced air usage, less harsh firing event and better trigger feel. Some results at 3000 psi and under would be nice when you do the unregulated tests. 
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on April 23, 2021, 11:49:14 AM
A question, what did you use for the stem? I just measured a normal 2mm HSS drill bit and the non fluted part is too short to be a stem for my Evanix.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 23, 2021, 02:21:05 PM
A question, what did you use for the stem? I just measured a normal 2mm HSS drill bit and the non fluted part is too short to be a stem for my Evanix.

https://www.amazon.com/gp/product/B00R1ISUN8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 (https://www.amazon.com/gp/product/B00R1ISUN8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1)

I cut it with side cutters, then polish the end on a vertical belt sander.  I do not harden the tips nor do anything special in attaching it to the peek poppet.  Drill a 1/16 hole in the peek, press it in with only an interference fit. 
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on April 24, 2021, 07:17:15 AM
A question, what did you use for the stem? I just measured a normal 2mm HSS drill bit and the non fluted part is too short to be a stem for my Evanix.

https://www.amazon.com/gp/product/B00R1ISUN8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 (https://www.amazon.com/gp/product/B00R1ISUN8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1)

I cut it with side cutters, then polish the end on a vertical belt sander.  I do not harden the tips nor do anything special in attaching it to the peek poppet.  Drill a 1/16 hole in the peek, press it in with only an interference fit. 

Thanks, ordered some. I was checking M2 grade 12.9 bolts but you can't get them long enough either. Bolts make great valve stems:

(https://live.staticflickr.com/65535/49448571383_478ab372d2_b.jpg) (https://flic.kr/p/2ikARvz)stem3 (https://flic.kr/p/2ikARvz) by abbababbaccc (https://www.flickr.com/photos/11843711@N08/), on Flickr
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 24, 2021, 10:19:11 AM
A question, what did you use for the stem? I just measured a normal 2mm HSS drill bit and the non fluted part is too short to be a stem for my Evanix.

https://www.amazon.com/gp/product/B00R1ISUN8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 (https://www.amazon.com/gp/product/B00R1ISUN8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1)

I cut it with side cutters, then polish the end on a vertical belt sander.  I do not harden the tips nor do anything special in attaching it to the peek poppet.  Drill a 1/16 hole in the peek, press it in with only an interference fit. 

Thanks, ordered some. I was checking M2 grade 12.9 bolts but you can't get them long enough either. Bolts make great valve stems:

(https://live.staticflickr.com/65535/49448571383_478ab372d2_b.jpg) (https://flic.kr/p/2ikARvz)stem3 (https://flic.kr/p/2ikARvz) by abbababbaccc (https://www.flickr.com/photos/11843711@N08/), on Flickr

You're welcome and agreed on bolts....   I used a long 4mm SHCS on my Extreme 457. 

Longer drill bits work as well, sometimes Amazon has great pricing on odd length drills. 

Here in the US it is amazing that you can often find 36 inches of drill rod from Grainger purchased via Amazon, for less than $10 including freight.

I am learning that my goal of having a dual caliber .257-.357 gun requires some compromise.  If one is only going to change barrel/bolt probe there are indeed compromises to be made.  In .257 it is much nicer to have the smooth, crisp shot cycle of the .270 valve throat and hammer in free-flight.    I haven't shot the .357 much with the smaller throat, but it basically performs like an OEM Bulldog (max~250fpe), albeit with much less hammer strike required vs the .375 throat.

I look forward to seeing how the smaller stem works for you.  I think it will do the things you want.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on April 24, 2021, 11:09:48 AM
I think I'll make a "cup" for the 2mm stem from a piece of 4mm steel rod. It gets glued over the stem end at the poppet end making it 4mm thick there and should prevent the stem from punching through the poppet thus allowing me to use PET-P as the poppet material.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 24, 2021, 11:18:06 AM
I think I'll make a "cup" for the 2mm stem from a piece of 4mm steel rod. It gets glued over the stem end at the poppet end making it 4mm thick there and should prevent the stem from punching through the poppet thus allowing me to use PET-P as the poppet material.

That should help, it is how Edgun poppets are made. 

I only use peek and in using peek have never driven a stem through a poppet.  There was one time where I didn't full press the stem in the 1/16 hole in the poppet---after a few shots the gun just went "click"....It had driven the stem into the poppet where there was no more stem protrusion.  Now I take careful measurements pre-pressing the stem and after to ensure the stem is bottomed out in the predrilled hole.  As long as the stem is full pressed into and bottomed out in the hole, it will not go any further in a peek poppet.

Edgun r3/r5 poppets ,showing a similar concept to what you describe.

(https://i.imgur.com/Khp1P2Q.png)
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on April 27, 2021, 07:39:42 PM
I think I'll make a "cup" for the 2mm stem from a piece of 4mm steel rod. It gets glued over the stem end at the poppet end making it 4mm thick there and should prevent the stem from punching through the poppet thus allowing me to use PET-P as the poppet material.

Quick update on the 2mm stem.  I have fired upwards of 100 rounds at over 3500-3800psi and max hammer strike without issue.  This occurred during a firelapping regimen (still chasing a barrel issue.)  I was using as-cast Arsenal 257388, which after embedding with lapping grit required max pressure to get them moving.  This was indeed a torture test of the 2mm stem peek poppet and as far as I am concerned it passed.

I need to cast up some more Arsenal 257388 so I can do more accuracy testing with them.  I do have an assortment of lighter ammo to test with, possibly tomorrow....
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on May 28, 2021, 05:33:11 AM
I made a 2mm stem valve for my .224 BSA. Unfortunately it didn't make much difference. I was able to loosen up the hammer spring a bit but there was no big difference I was hoping for. The original stem was 3.2mm so the area was reduced by 60% which should have considerable effect on dwell and the force needed to keep the valve open. BSAs do have very stiff valve springs though, perhaps the valve spring is now the dominating thing in valve closing event?
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on May 28, 2021, 04:20:35 PM
I made a 2mm stem valve for my .224 BSA. Unfortunately it didn't make much difference. I was able to loosen up the hammer spring a bit but there was no big difference I was hoping for. The original stem was 3.2mm so the area was reduced by 60% which should have considerable effect on dwell and the force needed to keep the valve open. BSAs do have very stiff valve springs though, perhaps the valve spring is now the dominating thing in valve closing event?

Interesting results.  Perhaps this means the throat isn't the primary restriction in porting?  I understand you were more thinking about the affect of closing force, but perhaps there is another part of the air path that is choking flow? 

I am letting my big bores (and my nitrogen supply!!) rest for a while.  Been enjoying 12-15fpe Prod based guns as of late....will get back to the big bores sometime between now and the fall.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rsterne on May 28, 2021, 05:40:03 PM
Quote
BSAs do have very stiff valve springs though, perhaps the valve spring is now the dominating thing in valve closing event?

That would be my guess.... Where is the smallest port equivalent, both before and after the stem change?....

Bob
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on May 29, 2021, 05:09:44 AM
Quote
BSAs do have very stiff valve springs though, perhaps the valve spring is now the dominating thing in valve closing event?

That would be my guess.... Where is the smallest port equivalent, both before and after the stem change?....

Bob

5.5mm ports and the valve tunnel was 6.4mm so bore size all the way. I need to dig up a BSA valve spring, any ideas how to measure the stiffness and compare it to the closing force of the valve stem? Or perhaps I should just ditch the spring and retest?
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on May 31, 2021, 04:03:31 PM
I don't think there is anything to lose in ditching the spring, if only for testing.  I have a couple guns that do not run valve return springs at all.....
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: rkr on May 31, 2021, 10:01:29 PM
I don't think there is anything to lose in ditching the spring, if only for testing.  I have a couple guns that do not run valve return springs at all.....

I tried with no spring and unfortunately self centering valve needs a spring to center, i.e. it didn't seal. It didn't seal with light spring either so I took off  some material from poppet to minimize spring tension with original spring and it held air. There was marginal reduction in cocking effort but not what I was hoping for. The problem is partly the Huma gauge/fill valve unit which does not allow quick burst of air in to the cylinder.
Title: Re: Regulated plenum vs reservoir volume .257 160fpe
Post by: mackeral5 on June 01, 2021, 03:42:45 PM
I don't think there is anything to lose in ditching the spring, if only for testing.  I have a couple guns that do not run valve return springs at all.....

I tried with no spring and unfortunately self centering valve needs a spring to center, i.e. it didn't seal. It didn't seal with light spring either so I took off  some material from poppet to minimize spring tension with original spring and it held air. There was marginal reduction in cocking effort but not what I was hoping for. The problem is partly the Huma gauge/fill valve unit which does not allow quick burst of air in to the cylinder.

That is interesting about the self-centering valve, I am not familiar with BSA's nor how that valve design works.  At least you were able to make a slight reduction in cocking effort.  Thanks for testing and sharing.