GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Privateer on December 25, 2016, 10:02:25 PM
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It concerns the Inovairtech Cartridges.
Given they have a set volume and do a complete dump of air on each shot.
Could you see a possible advantage to add a liner to reduce the volume say going from a .357 to a .257 bullet?
Or even going to a lighter bullet would a reduction in volume be worth testing?
I'm thinking a small reduction in volume but keeping the pressure up may help with the loud report in some cases?
It would be easy to add a small delrin ring inside to reduce the over all volume.
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Should make it slower and quieter. Report happens when the bullet "uncorks" from the muzzle and the air rushes out. So you could figure the internal volume of the cartridge, know the pressure, figure the volume of the bore, and figure out what the air's pressure at bullet exit would be.....starting with less volume at the same pressure would make for less pressure when the air expands to fill the bore and the bullet "uncorks".
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So what I'm thinking is sound then in a way.
:D
For all the math stuff? I'll be the first to admit if it involves more then 10 fingers and toes?
I'm not the guy.
I do have one of the carts ready to send to Bob. I figure he's the Guy to really give details on it.
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What exactly are you try to accomplish?
If it's a sound add a moderator. There isn't enough volume in the cartridge as it so I can't see making it any smaller.
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So you'd put a .25 valve and plenum in a .177 and expect good results?
I do believe you missed the whole point of my question.
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Yes putting 3,000psi in them would definitely be overkill in the cartridge for a .25. I would say pumping the cartridge to the best pressure for whatever you're going to shoot out of it.
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Keep in mind this Gun is not like other PCP's.
We have only a few limited ways to regulate it.
Pressure, volume, and MAYBE the spring that controls the firing pin.
Change the firing pin spring means you would not get a complete dump of all air.
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You aren't real clear on what your trying to do.
If it concerns anything with bullets there isn't enough volume. Cartridges all all the same size and nothing shoots at optimal speeds.
At EBR last year there was one shooting .30 pellets and it had a 38" barrel.
If your trying to shoot pellets lower the pressure
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The basic concept of a dump valve (which the cartridge uses) insures that the valve is still open when the pellet/bullet exits the muzzle.... The residual pressure at the muzzle shows up as report.... and can't add to the muzzle velocity, because Elvis has already left the building.... What that pressure is, depends on the ratio of cartridge volume to barrel volume, times the fill pressure.... The smaller the barrel volume, the greater percentage the residual pressure will be, compared to the fill pressure....
As an example, if the cartridge equals the barrel volume, the residual muzzle pressure will be 2250 psi.... The sad thing is, that if you closed the valve at the instant the bullet exits the muzzle, you would have the same velocity, and use only half the air.... which would double the efficiency.... Until I get a cartridge, I would only be guessing at the internal volume.... but generally speaking, if the valve is more than half the barrel volume, the efficiency is pretty poor.... With dump valve, big volume is needed for big power, but gives poor efficiency and a loud report.... To get efficiency you need small valve volume, but that means lower power.... You are correct, however, that for consistent performance between calibers, matching the cartridge volume to the barrel volume is the key....
Bob
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Packages go out tomorrow Bob.
I got sent away before I could mail a few weeks ago.
Again. I don't expect this platform will ever be a big FPE maker.
I do know it does what I want and need for what it is.
It can be tweeked as all AG's can be.
I just happen to be the nut to actually have it to play with.
;D
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Man, They ARE Good Looking AG's for sure.
Sadly, even a .22 or .25 typical PPC with NO LDC is L-O-U-D! :o
Knife
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Loud is not that much of an issue here.
I live in a small Village with no restrictions on shooting.
I'm just looking at the possibility that I'm wasting a lot of air.
Granted 20 pumps to hit 3000+ PSI is nice but do I need that all the time?
It might work out to restrict the volume of the carts for the .257 bullets and still pump to 3000 but less pumps.
And Yes! I'm a sucker for the TactCool!
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OK...made some assumptions....thought the basic idea was to still use the same pressure but reduce the volume of air in the cartridge rather than use the same volume and reduce the pressure.
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IIRC I read that the cartridge was 10cc. If that is true, that would make it about right for .25 cal IMO. However, 10 cc's is lacking volume to push a .357 bullet.
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There isn't enough air in the cartridges for any size bullet. When you go down in caliber size it becomes harder to make power. You have less surface to push on. There is a guy on this forum that has a 257 and it was way down on power.
10 cc is nothing. Basically you need 1 cc per fpe to be real efficient for a bullet and can get away with 1/2 for pellets.
I have asked twice what you are trying to do. I guess your trying to make it a 257
Your made a comment about running a .177 on a .25 setup.
Well yes in the bullet world. My 257 uses a .308 valve. The smaller the bullet the harder it is to.make power.
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A typical .257 barrel (24") is 20 cc.... It the cartridge is 10 cc, and filled to 4500 psi, and all the air is dumped quickly and efficiently, you should be able to drive a 70 gr. bullet like the 257420 into the 900s.... However, the same modelling suggests that the same volume and pressure could launch a 140 gr. in .357 in the 800s, and IIRC that was beyond what the MACR could do?....
Doug, while the (plenum) volume per FPE applies to conventional PCPs with a valve that closes before the bullet leaves the barrel, dump valves are pretty much bananas to apples by comparison, because you are using all the air.... In fact, the smaller the valve volume the more efficient, but of course the lower the power.... Using the same 24" barrel in .25 cal, and a dump shot of 4500 psi air with a 70 gr. bullet, consider these numbers for different valve volumes.... (each cc of air at 4500 psi is 17 CI of air at 1 bar)
1 cc .... 525 fps (42 FPE) at 2.38 FPE/CI
10 cc.... 928 fps (134 FPE) at 0.79 FPE/CI
100 cc.... 1082 fps (182 FPE) at 0.11 FPE/CI
If you closed the valve the instant the bullet left the muzzle, you would get the same velocity and FPE, but the efficiency would drastically increase with the larger valves....
10 cc.... 1.05 FPE/CI (25% of the air wasted)
100cc.... 0.57 FPE/CI (80% of the air wasted)
Bob
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From there website.
357 82 gr at 800 fps on 4500 psi
257 85 gr at 746 fps on 4500 psi
There .30 pellet has a 30" barrel and shoots 44 gr at 845 fps on 3400 psi. My .30 has 30" barrel and shoots 900 fps on 1600 psi and the reg chamber is not as larger as it should be.
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I would conclude from that the cartridge is less than 10 cc.... but I guess I'll find out when I get one.... It could also be that the diameter of the valve is severely restricting the airflow into the barrel.... Note I added some information on what "should" be available.... ie what you could get in your Condor with a 10 cc reservoir and a dump valve.... :o 8)
Bob
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Yeah I saw. Took me awhile to get info.
I don't know what they are doing but these guns have come and gone. The numbers and consistency were just not there.
It might not be using the whole cartridge already.
It was funny to see the one at EBR with a 38" just to get the speed and not have to fill to higher pressure.
Can't find the size. They say it's 103 mm x 20 mm
Maybe you can figure away to get more out of them
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Yeah, I never thought much of the design when they first came out.... immediately realized the limiting factors.... Some have been pretty enamoured about them, so after getting bashed initially I have kept quiet.... Those dimensions have to be outside, a cylinder that size is over 32cc.... I'm used to pumpers with dump valves, that is where I started modding airguns before I got into PCPs.... In my .22 Uber-Pumper I got 26 FPE (14.3 gr @ 900) from just 3.5 cc of valve volume in a 24" barrel (15cc) .... at probably half the pressure we are talking with the MACR.... so I know what you can get from a small (relative to barrel volume only 23%) dump valve.... The biggest problem with dump valves is that when you push the power, you need a big valve, and the efficiency goes in the toilet.....
Bob
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Thanks for the info and knowledge you Guys are sharing.
:D
Again. I KNOW this thing will not be a big power Gun.
I only have it because I got a good buy and I really did want something not everyone has.
Just like the SMG .22? Lots of air is wasted and I consider that the price of having some different fun.
;D
I have some .257 bullets ordered as I'd think those will be better given the design and shooting to 100 yards or so max.
There is very little, if any, info from anyone about possible tweeks or adjustments to this platform.
So there is that factor also. To learn and share what is learned.
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I have 67, 69, 74 gr 257 bullets. I only shoot 85 and 92 gr now.
Let me know if you want some.
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Knifemaker is going to make some of his .257's for me.
8)
One of the parts in the cart is made out of delrin.
I may change that out and do it with PEEK 1000 after reading another thread here at GTA.
Here you can see the part I'm talking about. That white part is the seal that is released to dump the air.
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1831.jpg)
The whole tube assembly moves forwards with the firing pin strike lifting the white part from the seat.
And I do apologize for not being able to be super clear on explaining things.
I am new to PCP's in general.
And the danged Cookies I was promised never showed up!
:)
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Not sure I see how it works? Does the air travel thu the stem?
If so I see why it doesn't work. Like a stock condor where the stem ID is to small to move enough air fast enough
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Yes. That stem has 4 holes to the left of the delrin part.
Once the firing pin strikes it lifts the delrin off it's seat and holds it open.
The air travels through the tube to behind the pellet/bullet in a total dump.
Here's a better pic.
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1833.jpg)
The spring only holds the transfer shaft to the rear and the forward seal with enuff pressure to hold air until you get the pressure building. After that the pressure in the cart does the holding.
You do need the Teflon tape! It will leak if it's not applied when you put the delrin part on.
Ask me how I know.
:)
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What is the OD of the stem and the ID of it?
Peek won't change anything for the seal that I know of. I use peek for its strength and only using a .020" seal surface
The ports look small. Making them longer might help. To get more air into stem if it's not to small already
Shouldn't need the tape if that o ring was doing its job.
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Good observations. Same stuff I'm thinking in some ways.
I'll mic the stem and get better pics of it.
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Here's a few Pics.
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1864.jpg)
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1863.jpg)
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1865.jpg)
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1862.jpg)
That stem mics out at .245 OD .165 ID
.075 is the thickness of the cart itself.
Maybe 2.0 for total length inside the cart.
.785 OD on the cart itself.
You should also see the slag I found in this cart in the one pic.
Time to take them all down to check that issue.
(Figured you all are tired of the Mr. Bubbles jammies so I wore some Camo)
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There is the problem. Just not enough flow. A condor stem is .217". The valve I sell is .260" and my 257 stem is .285"
Depending on what it's made of there is room open it up. At least to a letter F drill that is .257". Then elongate the ports at least 1 1/2 what they are.
No wonder these things never made any power.
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I'm not really looking to make more power.
Though that would never be a bad thing.
;D
I'm thinking I need to watch for a possible crushing of that tube if it's modded?
It has an outside air pressure inside the tube and whatever PSI is inside the cart.
And I can't find the post but I did read that they talked about a bigger cart in a limited edition Gun for more power.
Now say I made a larger transfer tube. That would reduce the inside volume of air.
Is that a viable trade?
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Certainly seems clear to me where the loss of power is.... ::) .... It looks like the total port area is pitifully small for a Big Bore, which is what they intended it for....
You are correct, each part has to be looked at for MSWP, you can't just go drilling out things and end up with them collapsing, imploding, or rupturing.... 4500 psi is a LOT of pressure.... It seems to me like there is a lot of "stuff" inside the cartridge, robbing it of air volume.... That's not a bad thing for efficiency, in the smaller calibers.... I agree, no need to change to PEEK, once that white seal is knocked off the seat, the material will make no difference.... and the firing pin obviously has enough power to do that at 4500 psi....
I think it may be possible to make this into a decent .257 cal.... not a rip-snortin' stomper like Doug's Condors, but if we can get it to push a 70 gr. into the 900s that could be pretty useful.... I'm looking forward to getting my hands on the bits and pieces, for sure.... Take Doug up on his offer of .257 cal bullets from 67-74 gr.... they should be just what you need....
If the stem is 0.245" OD x 0.165" ID, that only leaves a 0.040" wall thickness, so I would NOT start drilling it out, because as you say, before firing there is 4500 psi around it and only atmospheric pressure inside it.... Inside volume is about 10cc, minus the guts.... should be OK for a .257.... How long is your barrel?....
Bob
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Bob how would you figure the strength of the stem in the chamber? Says they are made of 303 stainless. I say 40,000 yeild but it's backwards on where the pressure comes from. Outside instead of inside
I used the wrong numbers in earlier post. I would open it up to .177" or .181" from .165". A #16 drill or #15.
Yeah I'm just thinking that you will be able to get more air out quicker which will make for higher fps. You can also just run lower fill pressure to equal what you have.
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I did some cheap calculations and I'm getting just under 10cc of usable volume.
I suspect it's actually lower then that.
I can see increasing it a small amount with work on that delrin area.
But really can't see any reason to do so at this time.
In .357 it's fine for me out to about 60 yards.
I do believe the .257 will be the more accurate out to 100 - 150 yards.
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OK. Say I drill one of the tubes out a bit.
Would a blanket of chain saw proof pants be OK as a safety measure?
I'd think it would just collapse the tube but I do like my eyes.
And with that?
I need to take all the carts down. I just found something I'm a bit concerned about.
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1870.jpg)
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Using the factory numbers you gave in .257, just increasing the through hole in the stem (if possible) to 3/16" (0.187") should give about another 50 fps with the 85 gr.... To get into the 900s with a 70 gr. will need a port of about 7/32" (0.219").... and who knows if you can get that big a passage through the fill fitting?.... As you go up in caliber beyond .257 cal, the numbers look much worse.... It might make a heck of a .224 cal bullet shooter, though....
Bob
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Waiting to see what Bob thinks of the safety factor.
Could be made out of 17-4 or 1144 and that wold make it about 3 times stronger and able to go thinner.
I use 17-4 on my 338 stem and it's only .019" thick. Crush factor is all I have to deal with though.
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(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1870.jpg)
See that area in the transfer tube? that is the first one I've seen.
I'll check all 6 carts for that.
I know the one going to Bob does not have that.
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Nice groove. So how thick is it at the groove?
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1st think I thought?
There's a shear point!
.235 is what that mics to.
That's .010 undersized from the tube itself.
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Now it's getting exciting!!
I'll need to get some more pics to show this all.
seems I have a mix of carts!!
:o
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/100_1871.jpg)
If you look close? the holes in the rear are smaller on that new cart transfer tube.
You saw it first at GTA Guys!
LOL
Now if you go back to the pic about the groove?
We know why it's there.
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That is the other big problem they have. Shot to shot consistency from cartridge to cartridge.
Now I see one reason why. Need to at least start with all the same type cartridges.
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I'm going to try to contact the original seller of this setup to see if I can get some info.
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UncleDevo sold it to Tims229 and has not been back to GTA since August.
I bought it from Tim.
Maybe Tim can give us a bit of back ground?
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This does explain some of the issues so far.
::)
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Uncle devo moved on to a .257 condor. I had his gun here a couple of months ago for a work over.
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Maybe you can get some history from him?
I did post on inovairtechs FB page but I'd bet that gets ignored.
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I have been trying to find a formula for external pressure, and it is NOT a simple thing to calculate.... For one thing, the length comes into play as a factor in the buckling load.... That is why external stiffening ribs are used.... to reduce the effective length.... I did find a calculator, but there is one variable I do not understand....
https://mathtab.com/app_id=1646
If we use 4500 psi, an ID of 0.165", and a yield strength of 40 Ksi (as Doug suggests) at 4:1 SF, so use 10,000 psi as the allowable stress, and no corrosion allowance.... we get 0.031" minimum wall thickness.... However, I do not know what value to use for the Coefficient "Y".... Using a value of 1.0 makes the minimum wall 0.026", and using 0.10 makes it 0.036".... The default is 0.4, giving the 0.031" wall.... I found the yield strength of 303 SS listed at only 30 Ksi (it is the yield that is the critical nuber for external pressure, as the failure mode is buckling, not explosion).... If we use 30,000 with a 4:1 safety margin that makes the allowable stress 7,500 psi, which using the default Y = 0.4 gives a wall thickness of 0.040".... Guess what, that is exactly what they used (neglecting the groove in one of them)....
OK, so if we use that calculator, 4,500 psi presure, with 7,500 psi stress, Y = 0.4, and increase the ID to 0.187", the wall thickness jumps up to 0.045", so the OD would be 0.277".... If we go to 13/64" ID (0.203"), the wall would be 0.049" giving an OD of 0.301".... and if we go to a 7/32" ID (0.219"), the wall jumps to 0.053" and the OD would be 0.325".... How about we use a stronger material?....
If we use 1144 stressproof steel, the yield strength is 100 Ksi, so a 4:1 SF we can use 25,000 psi as the allowable stress.... For the 0.219" ID, we get a wall thickness of only 0.018", which is an OD of 0.255".... Making a lot of assumptions about how good the calculator is, if the value of Y = 0.4 is valid (with the material change), we should be able to use a piece with the same OD of 0.245" and have an ID of 0.203".... that requires a 0.017" wall, so the OD would be 0.237, and we have 0.245" now.... It would seem that from a material strength point of view this may be possible.... but back up a minute.... A 0.017" wall thickness?.... That is REALLY fragile, and very prone to local damage or machining errors that would concentrate the stress, and cause a local buckling and collapse of the tube.... Using a stronger material may be just the WRONG way to go.... or maybe not.... I certainly don't know enough to make that call.... The only good thing here, is that when a tube buckles and collapses, it often doesn't rupture, it just gets squashed flat.... Could that flattened tube end up shot out the barrel.... I have no idea?.... Could it leak catastrophically and fire the bullet by itself.... I wouldn't bet against it.... ::)
Bob
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I get a .040 wall thickness on the internal transfer tube.
I measured 5 of them to be sure.
They are chrome plated.
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Chrome plated 303 Stainless?....
Bob
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All I can tell you Bob is a magnet will snatch it up.
I can drop a building within inches of where you want it just by looking at it.
That's what I do for a living.
I did learn long ago to seek out the experts for other stuff.
;)
Inovairtech states CR20 high tensile steel for most parts of the cart.
That would be the main shell and the transfer tube.
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Then it's not 303 stainless. I guess just the end pieces must be. The say they used CR 20 steel for the cartridge. Wonder if they used that for the stem?
I didn't have much luck on CR 20 steel. Unless it's cold rolled 1020?
What I did find puts it in the same strength as 303 basically.
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Yes. Just the end parts are SS.
Bob. A standard Hydraulic 10,000 LBS coupler is what you will need to pump the cart up.
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I won't be shooting it anyway, so no reason to fill it.... *LOL*....
I found the yield on 1020 CRS to be 50,800, so a 4:1 we would use 12,700 psi.... Using the calculator, that gives a wall of 0.026" for the current ID.... If we use a 3/16" (0.187") ID the wall would be 0.029", which gives an OD of 0.245", which is what the ones are that don't have the groove.... If it were mine, I would be prepared to drill it out to 3/16" ID and then enlarge the four ports to slightly greater area than that.... They would be equal in area if they were 3/32" holes, so they need to be at least that big.... That wouldn't leave much material between the holes if they are all in the same plane.... How big are the cross holes now?.... could they be doubled in length?....
Please remember, I'm not an engineer, these aren't recommendations for you.... I certainly wouldn't go any larger than 3/16" ID, and then only on the ones with no snap ring groove....
Bob
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I get about a .085 hole one the full spring transfer tubes and about a .078 on the others.
The .085 also have a taper of sorts.
Kind of like you'd do a port and polish to smooth air flow on an engine.
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Sounds like the full spring tubes have more potential.... If you drill one out to 3/16" there won't be a lot of material between the holes on the inside.... I would tend to lengthen the ports rather than make them a larger diameter.... You need to lengthen them about 1/32" (0.030") so that the four of them equal the area of a 3/16" hole.... (a bit longer might be even better).... Bear in mind, these changes will only buy you about 50 fps at 4500 psi.... but without making a transfer tube with a larger OD (and that may affect the spring and the seal) you can't do much more.... You can reduce the OD of the white seal to just larger than the seat (if it isn't already) and taper it so that the front end matches the spring OD.... That assumes you can reduce the diameter of the seat it sits against to the spring OD as well, and still achieve a seal.... Basically you are maximizing the internal volume and getting as much flow as you can.... You need to check at the front and make sure the through hole is at least 3/16" as well, right to the base of the bullet....
Bob
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You have 'compressor parts' on the way Bob.
;D
"I won't be shooting it anyway, so no reason to fill it.... *LOL*...."
I can see you building something just to shoot it.
;D
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You wish!
Bob
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Nah. Just figured you might like to pump it up and discharge it in some way.
:D
Was about to go buy some drill bits until I remembered David threw in a big bag of bits with the lathe.
So David AKA Rocker1 is my hero today.
;)
I'll take one of the carts and get it over the chrony as is for a base.
Then do one modification at a time and chrony it at each step.
There is room to slot the holes some.
I'll use Neilsen's 70 grn .357 to do tests.
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660.3 FPS at 4000 PSI with a 70 grn bullet is the base.
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Less than 70 FPE?.... YUK!
Bob
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Is that 357? That is way low
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Oh man, how come they effed up the design like this, I thought it was another copy / version of Robert Lane design where the case mouth is the effective port.
That's just plain poor and will never give good performance IMO.
The Lane cartridge has small chamber that the firing pin opens to back off the piston to open the cartridge valve.
Marko
Edit: picture. (http://i8.aijaa.com/t/00196/14309991.t.jpg) (http://aijaa.com/qAbKz9)
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Agreed. Lane cartridge is more what I was expecting when I heard it was a dump valve cartridge. Turns out it's essentially the same valve design as Crosman uses in the 1077 and 357 co2 guns....and not a blow open or dump valve at all. ::)
Lane cartridge is very similar to the Saxby cartridge.
https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US4531458.pdf
Al
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Pulled the barrel off to inspect it.
I found a lot of lead packed near the breech end so I suspect that some bullets are getting shaved in that area.
That build up would allow a gap that could be leaking air on firing.
I'll get it all cleaned out and shoot again with a bit smaller bullet to see if that helps.
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So the Lane (and Saxby) cartridges have a small pressure chamber at the back that holds the main valve stem forward.... Firing pin vents that and dumps the air and the main stem is driven back by the air pressure to open the valve at the front?.... Sensible design....
Bob
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Same cart filled to 4000 PSI with a 98 grn smaller diameter bullet.
647 FPS
Gonna fill again to 4000 PSI and try a JSB .35 81 grn
Rick used those for his reviews.
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Five years ago I was doing 116 FPE with 78 gr. EunJins with a modded Disco on 2400 psi.... ::)
Bob
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Yes Bob, I like the Lane design, pretty much same as the old brocok BACS system. But this Mac air cartridge is pretty much the stupidest design of any cartridges I have seen. And the lack of power pretty much proves it.
I would use the base the cylinder and coupling on this and make new innards for it.
The transfer port in the stem is too long and too small, takes forever to flow the amount of air in the cylinder.
Marko
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I think the ID is the problem way more than the length (barrels are much longer).... but we agree that the passage inside the transfer tube is way too restrictive....
Bob
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The length is dead space that eats volume from the cylinder and needs to be filled during a shot. Any port volume between the cylinder and projectile is bad when you have so little volume to begin with.
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True Dat!....
Bob
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Maybe a sabot of some kind in the tube?
I have some 1/4" Peek 1000 on the way for other projects so may give it a try.
Don't drill the tube out.
That was a total fail.
:(
It didn't collapse but it did bend and jammed.
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Where did it bend and how?.... How big did you go?....
Bob
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Did you drill it in a lathe?
Would be fun to play with one and see how much improvement can be had with different internals.
Maybe we'll see my version of the Mac rifle in the future...
Marko
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.257 barrel is back on it and I'll try some of KnifeMakers bullets in 70 grn 1st.
4000 PSI same cart.
640.3 FPS
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Really kinda sad, huh?.... ::)
One thing I'm learning from this, however.... is how to use smaller transfer ports in Lloyd's program to predict FPE levels.... Still working on it, but every piece of data helps.... 8)
What are your barrel lengths?....
Bob
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Really kinda sad, huh?.... ::)
One thing I'm learning from this, however.... is how to use smaller transfer ports in Lloyd's program to predict FPE levels.... Still working on it, but every piece of data helps.... 8)
What are your barrel lengths?....
Bob
Sad in that the Stated specs don't match up. But that's the norm now days.
Never expected it to being Honest.
I can say it's pretty accurate at 50 yrds no matter what round I'm shooting so far.
From their web sight...
.257
The barrel is precision hammer-forged moly steel and is 26" long. It is rifled (6 grooves) with a 1:14 RH twist with a bore of .250" and grooves of .257"
.357
The barrel is precision match grade molychrome steel and is 28" long. It is button rifled (6 grooves) with a 1:18 RH twist with a bore of .351" and grooves of .356"
I can tell you the .357 bullet samples I have are .358 or so.
KnifeMaker sent me a sample of .257's and the ones I've checked so far are .257 or so.
I got some 126 grn .357 Bob's Boattails here.
:)
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sorry. the .257 is about 80 grn.
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That brings me within 2 fps of your 640 with that bullet using Lloyd's spreadsheet.... more data needed to confirm, of course....
Bob
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I picked up a digital scale to weight the bullets. Would a more exact weight help?
I can also shoot the different bullets at different pressures.
2 FPS is darned close!!
:o
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61.7294334 grn .257 bullet at 4000 PSI
687.4 FPS
Gamma Master Chrony at 2 feet away from the muzzle.
I'm using the same cart to eliminate any possible changes between carts and testing for leaks after each fill to insure the pressure is true in each shot.
The pump is a G6 that shows true when hooked to a Dwyer 5000 PSI Gauge, the Hatsan At 44 gauge, and a gauge I bought from N-Forcer that reads to 5000 PSI.
If it reads 4000 PSI I have no reason to doubt it.
I think I'll drill out one of the lighter bullets base to near 40 grn and see what happens.
I'll post the final weight before I post the FPS.
Let's see how close you get to predicting the FPS Bob.
:)
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No point in going less than 0.1 gr, IMO, or 1 fps on velocity.... the Chrony isn't that accurate.... The data I need to refine the spreadsheet is an accurate inside volume for the cartridge, and the bore of the transfer passage at the most restricted point.... and also the internal volume that is NOT pressurized before firing as well (as that drops the pressure before it gets to the bullet).... Right now I'm using approximations....
Using different bullet weights and pressures to give more data points is always good.... as is data from more than one caliber.... If the spreadsheet numbers stay close to the empirical data, we may be onto something.... If the spread is too great, then it's more coincidence than good science.... Time will tell....
Bob
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50.9267826 grn .257 at 4000 PSI just to see what I get.
;D
You should be getting the stuff real soon.
Went through Chicago the 30th.
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Think I'm going to need to repeat this last test shot.
790.4 FPS?
Now I drilled the base of the bullet to lighten it so maybe that caused a better seal?
If so that may affect other bullets as well.
That probably also is worthless to the spread sheet?
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When the only thing I change is from 80 gr. bullet to 61.7 gr. to 50.9 gr. the velocity goes from 641 to 710 to 767 fps.... Those are only in the neighbourhood of a 3% error, which is still very good.... did you have a more accurate weight on the 80 gr. than "about 80?"....
Bob
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79.9396163 grn
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Close enough.... that 0.1 gr. changes nothing.... (0.4 fps)
Bob
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Seems pretty clear the lighter bullets is what to look at with this Gun to go for NUAH with it.
JSB .25 29.39 grn at 4000 PSI
1004 FPS
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I assume you mean 25.39 gr. and I get 958 fps for that.... still within 5%.... and I don't have accurate volumes yet.... We need to figure a way to get larger ports....
Bob
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I think that sacrificing little volume for better flow will gain some velocity. So drilling out the front part of the case and making a bigger transfer tube seems like the best option if you like to use the current valve type.
But still if you have lathe I would opt for similar internals as the Lane cartridge.
Not too hard to do just couple of parts to make and modify both end caps.
Marko
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I received the MAC Cartridge today, and carefully measured all the volumes.... Although the housing has a volume of 10.96 cc, the total volume once you subtract all the internals is 7.99 cc.... OK, maybe 8 cc.... ::) .... I changed the volume to that in Lloyd's calculator, and at 4500 psi, in .257 cal, with a 26" barrel with bore-size porting, and assuming excellent efficiency, you would do very well to achieve 140 FPE with a 70 gr. bullet.... With the 0.165" port through the transfer tube, and the same bullet and pressure, it works out to more like 90 FPE (760 fps) at 4500 psi....
Again assuming bore size porting, but in .357 cal, that tiny 8 cc reservoir could in theory hit 210 FPE at 4500 psi in a 28" barrel with a 105 gr. bullet.... However, with the 0.165" port it has, it's more like 100 FPE (650 fps) at 4500 psi....
For the bullets you tested, at 4000 psi with the stock 0.165" port and 8 cc, Lloyd's Spreadsheet get the following results for a "lofty goal"....
70 gr. in 28" .357 cal = 725 fps (you got 660 = 91%)
98 gr. in 28" .357 cal = 634 fps ( you got 647 = 102%)
79.9 gr. in 26" .257 cal = 686 fps ( you got 640 = 93%)
61.7 gr. in 26" .257 cal = 762 fps (you got 687 = 90%)
50.9 gr in 26" .257 cal = 821 fps (you got 790 = 96%)
25.4 gr. in 26" .257 cal = 1050 fps (you got 1004 = 96%)
Other than the one .357 cal bullet (98 gr. @ 647 fps) your results average 93% of the prediction from Lloyd's spreadsheet.... That's pretty typical for what is achieved by many PCPs.... It is obvious that the port diameter (ie the ID of the transfer tube) is the big problem here.... The only way I can see to get to bore-size porting would be to redesign the internals like what is done in the Lane or Saxby Cartridge.... I have no idea if it would be possible to convert the current MAC Cartridge, or it a complete redesign would be required....
Bob
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Just for the fun of it, calculate the power with bigger tube inside the cart, big enough for barrel size port. How much volume is lost and what would the power might be?
Maybe we can find some kind of mid point on power vs lost volume for bigger transfer tube.
Marko
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We don't really have good math for how thick the tube wall has to be to resist crushing.... but it would have to be at LEAST as thick as what is needed to resist inside pressure with a good safety margin.... When we calculate that, it is less than the 0.040" used in the existing tube, which makes me nervous, because increasing the diameter normally means you need a thicker wall too.... Keeping the same wall thickness to ID ratio might be better.... That would work out to (0.257/0.165) x 0.040= 0.062".... That means a 3/8" OD tube, instead of 1/4" OD.... The portion of the tube between the Delrin seal and the front seal is 1.7" long, so right now that is 1.32 cc.... At a 3/8" OD, it would be 3.10 cc, which would reduce the volume from 8 cc down to 6.2 cc.... and that is assuming you could keep the Delrin part the same size.... Right now there is only a 0.077" gap between it and the ID of the housing.... I wouldn't want to make it much less or flow around it could be problematic.... You also have to assume that the four holes that flow air into the tube can be made large enough, of course....
In addition, I made one error in the inputs to Lloyd's spreadsheet.... I neglected the lost volume inside the 0.165" ID tube, into which the air in the cartridge must expand before it ever gets to the bullet.... This, of course drops the pressure.... a LOT.... In the stock cartridge, it drops 10%.... With the larger tube, reducing the cartridge volume from 8 cc to 6.2 cc.... and having 2.4 times the internal volume for that smaller amount of HPA to expand in.... the pressure now drops over 25% before ever reaching the bullet.... Here are the corrected numbers for the bullets tried at 4000 psi.... As you can see, Lloyd's model is even closer to reality, with the correction for the expansion into the transfer tube dropping the pressure....
70 gr. in 28" .357 cal = 702 fps (you got 660 = 94%)
98 gr. in 28" .357 cal = 614 fps ( you got 647 = 105%)
79.9 gr. in 26" .257 cal = 659 fps ( you got 640 = 97%)
61.7 gr. in 26" .257 cal = 730 fps (you got 687 = 94%)
50.9 gr in 26" .257 cal = 785 fps (you got 790 = 101%)
25.4 gr. in 26" .257 cal = 993 fps (you got 1004 = 101%)
If we do the same process, but substitute a larger transfer tube, with a 3/8" OD and a 0.257" ID.... ie the cartridge volume is now only 6.2 cc, with a larger pressure loss.... we get....
70 gr. in 28" .357 cal = 790 fps
98 gr. in 28" .357 cal = 690 fps
79.9 gr. in 26" .257 cal = 744 fps
61.7 gr. in 26" .257 cal = 824 fps
50.9 gr in 26" .257 cal = 887 fps
25.4 gr. in 26" .257 cal = 1121 fps
As you can see, these numbers represent a significant increase in power, by using a larger transfer tube to increase the flow, even though the volume of HPA in the cartridge is reduced.... The velocity increases 13%, and the FPE by 27%.... If we use a 5/16" OD tube, drilled to 0.209" (same wall proportions) the cartridge volume ends up at 7.2 cc, and the pressure loss becomes 17%.... A quick check using those numbers results in velocities in between the above, so it seems that going for bore area porting (for the .257 cal) is better than looking for a compromise.... This of course is dependant on being able to build it.... Right off the bat, building the front sliding seal would appear to be an issue.... with a 3/8" ID and a 0.51" OD to fit through the female threads in the cartridge.... Perhaps a Metric O-ring could be used for the dynamic seal there?.... I dunno.... Practical considerations may limit the tube OD to about 5/16".... then drill the center out until it fails and back off a bit.... ::) .... Even that change would require a redesign of the Delrin part, as it is currently installed on 5/16" threads....
Bob
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Thanks Bob!
That's why I sent you one of the carts.
I'd probably suffer an embolism in my brain some where trying to do all that math!
:o
So a question comes to mind about the material for the tube.
Would Titanium be a better choice to use if one kept the same wall thickness to ID ratio?
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A high tensile steel, like 1144 Streesproof (which machines well), would be a good choice.... The tensile and yield are similar to Titanium, and we don't care about the weight.... You should PM Lloyd and ask him what would be the best material to use, he's got much more experience than I do.... I think if you use about a 0.050" wall with a 5/16" OD or a 0.060" wall with a 3/8" OD you should be fine.... Your challenge will be figuring out how to mount the Delrin seal on the sliding transfer tube without making the wall (of either part) too thin.... As I mentioned, if you go whole hog and try and fit a 3/8" OD tube, even if you could figure out how to do the Delrin part (the poppet seal) you will be running out of room for the Dynamic (sliding) seal at the front end of the rod.... The OD of that (brass) part is limited by the ID of the threads in the outer housing.... It doesn't need much of a lip to retain the O-ring, as the seal is at the inner corner, between the sliding transfer tube and the back of the front end.... Of course you may also need to enlarge the sliding seal at the back, where the firing pin hits the end of the sliding transfer tube.... unless you can put a shoulder in the back end of the tube and stay with the size it is now?.... That might be possible....
Incidently, as you should be getting more FPE from less air, the efficiency would therefore increase.... an added benefit.... BTW, I didn't factor in the wasted volume behind the Delrin poppet, around the area where the holes are in the transfer tube.... That causes an additional pressure drop on firing.... All in all, it's a pretty strange design.... ::) .... I think when you start working on it, you will find that 3/8" OD won't work, and that even using a 5/16" OD may be a challenge.... However, that should increase the port to at least 13/64", and I think you can probably get away with 7/32" (0.219").... even though that drops the wall down to 0.047".... That might put you close to 90 FPE with the 61.7 gr. bullet @ about 800 fps.... or about 85 FPE with your 50.9 gr. bullet at about 860 fps.... (both at 4000 psi) either one getting close to 1.0 FPE/CI.... which is pretty good for a dump setup.... Add about 40 fps at 4500 psi.... and you should be tickling 100 FPE....
IMO, even considering a caliber larger than .257 is a waste of time....
Bob
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Say I could fill the inside of the tube with a foam plug at the rear just forward of the 4 holes,
then fill with water and another foam plug to hold it?
Water suffering less compression is my crazy thinking.
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You just added the weight of the water to the weight of the bullet.... as both will now have to be accelerated out the muzzle.... You would end up with a slower bullet, and some very high speed water.... and a rusty barrel....
Also, if the tube collapsed, it would just push the bullet out of the nose of the cartridge.... along with that water and the foam plug....
Bob
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OK.
I admit that was a Village Idiot thought.
;D
Gotta earn my pay some how.
:P
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Looking at the pictures, I say it wouldn't be too difficult to convert these to the Lane type.
Why didn't they use stronger tube and thinner wall to get more volume to the cart is beyond me.
Marko
Quick calculation and 4130 could be used, 20mm od and 2mm wall gives around 5000psi wp on safety factor 3. 80k psi avarage tensile strength used on calculation.
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That is exactly the ID they are using, Marko.... The space between the threads is bored out to 16mm (and a VERY rough job it is, too).... If anything, the roughness of the inside boring job concerns me because the local stress risers where the grooves are from the machining will greatly reduce the safety margin....
Bob
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Whatta... why use m14 threads then? Now I'm confused. Just adding complexity and machining cost to make these things.
So it's m14 and then it opens up to 16mm, then back to m14 again? Did they bother to radius the corners?
M18x1 and O-ring after the thread would make much more easier to manufacture and you could use readily awailable tubing.
Marko
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Yep, 14mm up to 16, back to 14..... Moving the O-ring inboard of the threads would have cost length, and therefore volume inside.... Since the O-ring is at the outer end, outboard of the threads (which are under pressure), they didn't want to cut into the wall by using 18mm threads in a 16mm ID tube.... I think the current arrangement is shorter overall, for a given internal volume, which is why they used it....
Radius?.... I doubt it, since the inside looks like it was cut in a single pass with a dull tool bit.... you have NO idea how rough it looks.... ::)
Bob
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Well there is 6 threads on those now, it doesn't take so much more room to make it the other way around, 1mm lip before the o-ring to keep it in place when cart is empty, and the thread can start just about 1mm after the o-ring.
And converting to different valve design you don't need the tube, just a stem.
Darn, now I think I hafto make one or two of those carts to test.
Marko
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https://patents.google.com/patent/US20150013656A1/en (https://patents.google.com/patent/US20150013656A1/en)
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/1.png)
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/2.png)
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Thanks Jeff.
Well that is revealing, not much room for air is there... What was the moment in time they decided to go with this design. The cutaway tells it all, not much to do here but use the outer dimensions and forget the internals if you want any power out of it.
This'll be a long build for sure, and couple of projects before this.
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Part # 31 is not correct for the actual carts.
I'll see if I can draw the proper image of the current parts.
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Correct, Part #31 has the O-ring in contact with the transfer tube (54) AND the inside surface of the front end (45-46), which is flat on the back, flush with the inside of the threads, not recessed.... The actual #31 is a brass disc, 1/8" thick, with a lip around the outer edge to contain the O-ring, which is slightly proud of the end of said disc.... The O-ring used is a # 010, which is 1/4" ID x 0.070" (3/8" OD), and seals in the inner corner, where the transfer tube slides through the front end housing.... it is a dynamic (sliding) seal.... The O-ring is held in contact with the front end by the valve spring, and air pressure....
Bob
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Another part that may not be correct is the transfer tube part #54
I have 2 different versions.
The best version has the larger 4 holes and some what beveled on the edges.
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I need to do some checking on the cart and how much space is there to work with but here's another Village Idiot question.
:D
Say I could add a washer to kind of extend the cart?
I can add the same washer thickness to the barrel to allow for a proper fit.
That would increase the inside volume a tad.
Say I cut the Delrin seal back to add volume also.
A slip fit spacer to keep the pressure for what I remove.
If the Delrin proves to weak? I have Peek 1000
So something like this.
(http://i108.photobucket.com/albums/n12/privateer_2006/Air%20Rifles/MACR/Maybe.jpg)
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You have created another leak path between the front housing and the washer, the O-ring will now seal between the washer and the main body tube.... You might be able to do it by using a thinner O-ring gland so that the O-ring squashed out wider and could seal both gaps.... but the clearance between the washer and housing would have to be less than 0.003" or the O-ring will extrude into it and fail....
Yes, you could shorten the Delrin seal, providing you can still create a seal between it and the transfer tube it threads onto.... However, you are only talking maybe a percent increase in volume....I doubt your Chrony could consistently measure the gain....
Bob
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One thing you can do, turn down part 59 to spring od and taper the delrin to the same dimension leavin a constant radius to the sealing surface. It should increase flow.
Marko
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Yep, I noticed that when I first saw the cartridge.... It might reduce turbulence at that point, but would do nothing for the flow at the other end of the poppet (Delrin).... Basically, it couldn't hurt....
Bob
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Has anybody tried going to the manufacturer with this information yet and asking for an explanation? My "couple" of questions would be:
-Why do you publish such a high fps for a given weight bullet, when real world tests are not corroborating?
-Why is there so much leading in the breech end of the barrel? Bullets getting "shaved" definitely increases the drag on the bullet as it passes through the barrel and could definitely affect performance.
-Why are their two different designs of the cartridge? One has a shorter spring, a groove, and smaller transfer ports south of the delrin seal, while the other has a full length spring.
-Which cartridge is the "current version" that is being sold to customers, and are the two versions marked different in your inventory so that you know what you are sending people?
-Why are there no videos showing a live chronograph test with common pellets (say JSB .35's or the nosler ballistic tips)? This may dispel rumors about how underpowered the gun may be.
-Why is the transfer pin so rough on the inside? Do you manufacture in house or do you outsource some of your parts? If the transfer pin was chrome plated I would imagine that the inside was as well, so it should have been smooth. (This doesn't surprise me though as a Hatsan owner my 135 in .22 had a significant amount of factory negligence when it came to the finish of many of the components. When I pulled the piston seal off it had flecks of metal embedded in the plastic!)
I don't think anybody would get anywhere asking questions about the design and why they went that way rather than another. If they have the time/effort/money to patent the cartridge then it had been in the design and prototyping phase for a long time and they are obviously heavily invested in their "invention." It would be like questioning somebody why they chose to raise their children they way they did lol. ;D
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Well their invention is not theirs to begin with, they just made it bigger and used the most inefficient way to do it.
Those aircartridges go way back to old English patent around 1872 so it's nothing new. That is why I have been wondering why that design, and not something a bit more modern?
Legal issues, easy manufacturing and more profit?
I'm not bound by any of those so let's see what can be had with some time.
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Its a shame they didn't spend more time in R&D before launching the product. Talking to David Priestly the owner/inventor on the phone made me realize that he really thinks those MAC cartridges are the best thing since sliced bread. I doubt they would have a significant overhaul of the cartridge ever. And the fact that they didn't put a safety on the gun is just plain negligence in my mind... If I were ever to take that gun into a hunting situation I would want it to be ready to go at a moments notice, and I don't like the idea of walking around with a loaded gun ready to go off without the option of a safety. I mean c'mon how hard would it be to engineer a safety into that thing!