bulk co2 ?? self regulating ?//? any help appreciated-co2 masters

[kj]

hi, i have a bunch of co2 guns that run on cartridges and had one that ran on a 9oz paintball tank. i just changed one rifle to bulk fill co2, filling the stainless 2260 tube. with carts it was shooting 700-712 fps for 27 shots, very consistant all the way through the cart. this morning i bulk filled it, i got about 2.5 oz of co2 into the tube.

i started shooting over my chrony, my first shots were 593, i adjusted the pre-load and throw and in a couple shots had it at 712 fps. nice place for what i'm doing. it stayed about there for 10 shots or so, then the fps started climbing . the increases were gradual, but by the time i got to shot 80 the rifle was shooting 758fps, stayed in that area awhile and started dropping off. by shot 97 i was back at 700fps.

the temp was 90*, pellets jsb 8.44. i shot pretty mechanically. load, aim, shoot..repeat. the rifle never got cool, even shooting at a fairly quick pace.  and once it started shooting over 720 i'd hear a funny noise, like a spring vibrating or something. i don't own any pcp's but shot a few , never heard that ping, can co2 ping ?

i want my rifle to shoot more consistantly, not rise up like that. tuning suggestions ?

thanks
kj

[Bentong]

Try here > http://www.gatewaytoairguns.org/GTA/index.php?topic=37689.0

[kj]

thanks bentong, doesn't really adress the issues i'm have with the climbing velocity. and what to specifdically do to address this issue. bobs chart shows the different strings starting out and staying about the same level, then dropping off. this is what i'm used to working with co2.

my rifle has a boss bulk valve, known gas hogs, should i switch to a disco valve ?

peace
kj

[cobalt327]

You might want to research “de pinger” or "deping" to address the sound you’re hearing. If I understand correctly it’s caused by a resonance when the hammer contacts the valve stem.

I’m not qualified to speak about changing the shot string curve but I'm guessing someone w/experience in this will check in shortly.

If you plan on doing a lot of testing, one way to keep track of changes is to use Excel by putting your shot string in a column and use the graphing feature to create a "line chart". This makes comparisons easier.

Good luck.

[kj]

You might want to research “de pinger” or "deping" to address the sound you’re hearing. If I understand correctly it’s caused by a resonance when the hammer contacts the valve stem.

I’m not qualified to speak about changing the shot string curve but I'm guessing someone w/experience in this will check in shortly.

If you plan on doing a lot of testing, one way to keep track of changes is to use Excel by putting your shot string in a column and use the graphing feature to create a "line chart". This makes comparisons easier.

Good luck.

hi, thanks. i'm familiar with the ping idea in pcp, but never heard of it in co2. funny cuz my shot curve looks more like a pcp than co2 rifle. excell...lol...sounds like something i know nothin about

peace
kj

[cobalt327]

Might not apply to co2, sorry. I've heard of scopes causing a similar sound...

[BillK]

Not sure how/if this applies but, is the CO2 cold right after filling?  If so, would this explain the lower fps shots at the beginning?
Just a "shot in the dark".

[Rob M]

sounds like you may need a lighter hammer string , the  high numbers you are getting are incredible.. Co2 to some degree is self regulating , was the gun sitting in the sun over the duration of the string?? were you shooting " snow clouds " in the higher range of the curve?In the phillipines, co2 is ideal for shooting so temp may have been an iissue

[fivestar45]

kj
You are picking up speed as the gas temp drops. So to even things out my guess would be a bit more spring in the striker. I really doubt that you need the extra volume of a boss valve, I'd go with a Disco valve and if possible lighten the striker a bit. Are you using a hard stem, or a soft one? The hardest one that will seal would be best for you.

[kj]

Not sure how/if this applies but, is the CO2 cold right after filling?  If so, would this explain the lower fps shots at the beginning?
Just a "shot in the dark".

no, the tank i filled from got cold and i had to stop and let it warm back up to get a good fill. and the rifle sat an hour or 2 before i had a chance to shoot.

thanks for the input, every idea helps
kj

[kj]

sounds like you may need a lighter hammer string , the  high numbers you are getting are incredible.. Co2 to some degree is self regulating , was the gun sitting in the sun over the duration of the string?? were you shooting " snow clouds " in the higher range of the curve?In the phillipines, co2 is ideal for shooting so temp may have been an iissue

the spring is a standard 2240 spring, the hammer is a p-rod hammer/striker, lighter than a 2249 hammer. i hardly had any preload on it , and the striker was about a third out, so throw was 2/3 striker possibility. i have no doubt if i crank up the pre-load and lengthen the stroke i could get over 800fps with the 8.4 exacts.

have you ever heard of a co2 rifle pinging ?

thanks
kj

[kj]

kj
You are picking up speed as the gas temp drops. So to even things out my guess would be a bit more spring in the striker. I really doubt that you need the extra volume of a boss valve, I'd go with a Disco valve and if possible lighten the striker a bit. Are you using a hard stem, or a soft one? The hardest one that will seal would be best for you.

hi anthony, the boss valve has a disco stem ...i think. i'm not sure on that though.  i have disco valve stems on hand though. and disco valve. i have plenty room left to increase pre=load, and or change the throw. the hammer i'm using is the p-rod hammer/striker set-up, same one in the challenger.

so if i up the pre-load and start at a higher fps do you think it will even out ? i'll try switching out the valve to the disco valve. and open up the boss valve and see what stem it has. i thinjk this boss valve will be great for my .25's though..lol

what about the ping sound ? sounds almost like a spring vibrating or something ?

have nice day
kj

[dv8eod]

This is a shot in the dark, but you might be getting liquid in the valve at the beginning of the shot string. When i tried bulking the 2240, I had that issue and got a rising curve. I don't really know how to explain it, but it's like the liquid isn't receiving enough time to expand to a gas, and can't expand fast enough to let the gas be the propellant. It takes up room in the valve allowing only a little of the already expanded gas to do it's portion, while the liquid helps keep the bit it's touching cold and still in a liquid state.

My procedure is to put the hipac in the freezer for awhile before mounting on the gun to get as much liquid into it as possible. Then I try to hold it where the liquid is away from the valve while loading. Once I get enough space in the hipac things tend to smooth out and then drop off.

I haven't figured out how to do it yet, without adding more parts to the gun, but I do believe that bulk filling CO2 would benefit from having an expansion chamber/plenum like the paintball guys do. It would guarantee only gas in the valve and straighten out the shot string more in line with using a cart.

Given the temps, I would have to say a slightly stiffer hammer spring might be in order. If it's one of the guns you took over with you, you probably tuned it here at a lower temp/pressure and taking it over there with higher temps, you're getting a higher pressure.
Terry

[rsterne]

Two possibilities.... either....

1. Your CO2 charge had not reached your (rather high) operating temperature when you started shooting.... and as the gun gradually warmed up the velocity went up.... This would be "normal" for CO2....

2. Your gun is indeed "self-regulating" over the temperature range you have.... As the temperature drops as the CO2 boils off and cools, the pressure drops as well.... At the beginning of the string, when the pressure is high, the valve is not opening fully, and the velocity is low.... As the gun cools, and the pressure drops, the velocity increases.... When the temperature stabilzes, the velocity plateaus.... Once the liquid CO2 is exhausted, the pressure starts to drop further, and the velocity declines, just like in a PCP at the end of the bell curve....

If you are experiencing the latter, increasing the hammer spring tension will flatten the shot string, but increase the velocity and reduce your shot count.... If you like the flatter string, but want less power and more shots, then install a smaller transfer port....

Bob

[pecor]

This is a shot in the dark, but you might be getting liquid in the valve at the beginning of the shot string. When i tried bulking the 2240, I had that issue and got a rising curve. I don't really know how to explain it, but it's like the liquid isn't receiving enough time to expand to a gas, and can't expand fast enough to let the gas be the propellant. It takes up room in the valve allowing only a little of the already expanded gas to do it's portion, while the liquid helps keep the bit it's touching cold and still in a liquid state.

Terry Hit the nail On the Head!!  And I Agree, That's your problem. That's one of the pitfalls of tube Bulking no plenum chamber. Put a QB or JDS drop block and add a tank problem solved.                                                                     

 

[kj]

Two possibilities.... either....

1. Your CO2 charge had not reached your (rather high) operating temperature when you started shooting.... and as the gun gradually warmed up the velocity went up.... This would be "normal" for CO2....

2. Your gun is indeed "self-regulating" over the temperature range you have.... As the temperature drops as the CO2 boils off and cools, the pressure drops as well.... At the beginning of the string, when the pressure is high, the valve is not opening fully, and the velocity is low.... As the gun cools, and the pressure drops, the velocity increases.... When the temperature stabilzes, the velocity plateaus.... Once the liquid CO2 is exhausted, the pressure starts to drop further, and the velocity declines, just like in a PCP at the end of the bell curve....

If you are experiencing the latter, increasing the hammer spring tension will flatten the shot string, but increase the velocity and reduce your shot count.... If you like the flatter string, but want less power and more shots, then install a smaller transfer port....

Bob

hi, i think #2 is more likely. the gun sat for over an hour, maybe 2 before i started shooting. if i go with a smaller transfer port should i still increase the spring tension ? a flat string is paramount to me. even if i have to sacrifice shot count.  and is the noise i'm experiencing the same ping as pcp's get ?

thanks
kj

[kj]

This is a shot in the dark, but you might be getting liquid in the valve at the beginning of the shot string. When i tried bulking the 2240, I had that issue and got a rising curve. I don't really know how to explain it, but it's like the liquid isn't receiving enough time to expand to a gas, and can't expand fast enough to let the gas be the propellant. It takes up room in the valve allowing only a little of the already expanded gas to do it's portion, while the liquid helps keep the bit it's touching cold and still in a liquid state.

Terry Hit the nail On the Head!!  And I Agree, That's your problem. That's one of the pitfalls of tube Bulking no plenum chamber. Put a QB or JDS drop block and add a tank problem solved.                                                                     

terry did make a good point. i'm considering how to make a plenum space before the valve . i had a tanker rifle before and it was very consistant and easy to tune. i am planning on making a couple bottle guns soon as i find some nice wood here, but cutting this rifle is out of the question.

thaks
kj

[kj]

This is a shot in the dark, but you might be getting liquid in the valve at the beginning of the shot string. When i tried bulking the 2240, I had that issue and got a rising curve. I don't really know how to explain it, but it's like the liquid isn't receiving enough time to expand to a gas, and can't expand fast enough to let the gas be the propellant. It takes up room in the valve allowing only a little of the already expanded gas to do it's portion, while the liquid helps keep the bit it's touching cold and still in a liquid state.

My procedure is to put the hipac in the freezer for awhile before mounting on the gun to get as much liquid into it as possible. Then I try to hold it where the liquid is away from the valve while loading. Once I get enough space in the hipac things tend to smooth out and then drop off.

I haven't figured out how to do it yet, without adding more parts to the gun, but I do believe that bulk filling CO2 would benefit from having an expansion chamber/plenum like the paintball guys do. It would guarantee only gas in the valve and straighten out the shot string more in line with using a cart.

Given the temps, I would have to say a slightly stiffer hammer spring might be in order. If it's one of the guns you took over with you, you probably tuned it here at a lower temp/pressure and taking it over there with higher temps, you're getting a higher pressure.
Terry

hi terry, do you think if i took a piece of aluminum with a small hole at the top , that was o=ring sealed to the tube , and place it in the tube an inch or 2 before the valve , that it would create a plenum /expansion chamber good enough?  do you think i'd still need it afetr making changes anthony and bob suggested ? the valve i'm using is very open, like a big funnel. the disco valve i'm going to try is pretty flat in front with a smaller hole.

peace
kj

[dv8eod]

This is a shot in the dark, but you might be getting liquid in the valve at the beginning of the shot string. When i tried bulking the 2240, I had that issue and got a rising curve. I don't really know how to explain it, but it's like the liquid isn't receiving enough time to expand to a gas, and can't expand fast enough to let the gas be the propellant. It takes up room in the valve allowing only a little of the already expanded gas to do it's portion, while the liquid helps keep the bit it's touching cold and still in a liquid state.

My procedure is to put the hipac in the freezer for awhile before mounting on the gun to get as much liquid into it as possible. Then I try to hold it where the liquid is away from the valve while loading. Once I get enough space in the hipac things tend to smooth out and then drop off.

I haven't figured out how to do it yet, without adding more parts to the gun, but I do believe that bulk filling CO2 would benefit from having an expansion chamber/plenum like the paintball guys do. It would guarantee only gas in the valve and straighten out the shot string more in line with using a cart.

Given the temps, I would have to say a slightly stiffer hammer spring might be in order. If it's one of the guns you took over with you, you probably tuned it here at a lower temp/pressure and taking it over there with higher temps, you're getting a higher pressure.
Terry

hi terry, do you think if i took a piece of aluminum with a small hole at the top , that was o=ring sealed to the tube , and place it in the tube an inch or 2 before the valve , that it would create a plenum /expansion chamber good enough?  do you think i'd still need it afetr making changes anthony and bob suggested ? the valve i'm using is very open, like a big funnel. the disco valve i'm going to try is pretty flat in front with a smaller hole.

peace
kj

Honestly, I don't know how to go about it. When I was paintballing, it was simply putting a tube/handgrip between the tank and the valve. Liquid CO2 would still enter it if shook around, but it turned to gas pretty quick. It was held in a vertical orientation. I know it's the same principle as a pcp, but it's 2 different mediums (gas/liquid). I can't resolve how to keep a pressurized liquid in a horizontal attitude from being pushed into an open area. If a valve is added, no matter the state, the pressure would open it. The only thing I can really think of is a vapor seal type setup, and I have no clue as to how to obtain one, let alone install it. I do know they make osmosis screens for various gases, but would a screen that allows gaseous CO2 to pass also allow the liquid to pass?
The only thing I've managed to come up with was tipping the gun so the liquid was away from the valve until firing.
Sorry, that's all I got...
Terry

[fivestar45]

kj
You are picking up speed as the gas temp drops. So to even things out my guess would be a bit more spring in the striker. I really doubt that you need the extra volume of a boss valve, I'd go with a Disco valve and if possible lighten the striker a bit. Are you using a hard stem, or a soft one? The hardest one that will seal would be best for you.

hi anthony, the boss valve has a disco stem ...i think. i'm not sure on that though.  i have disco valve stems on hand though. and disco valve. i have plenty room left to increase pre=load, and or change the throw. the hammer i'm using is the p-rod hammer/striker set-up, same one in the challenger.

so if i up the pre-load and start at a higher fps do you think it will even out ? i'll try switching out the valve to the disco valve. and open up the boss valve and see what stem it has. i thinjk this boss valve will be great for my .25's though..lol

what about the ping sound ? sounds almost like a spring vibrating or something ?

have nice day
kj

kj, pretty much all of my rifles "Ping" The only one that might not is the alum tube Disco with the Don Cothran valve.
As far as the striker weight goes, I'm pretty sure the P'rod with the hammer installed weighs just about the same as the oem 2240 +- 58g. Another thing to note is if you are using that factory hammer/stroke adjuster, even with it backed out to where it is flush against the striker face you will loose about .060" of stroke if you use a standard length Disco stem. I use those strikers but I use a 1/4x28 allen set screw with the face ground flat for the stroke adjustment. To further lighten them I also bore them and use a Delrin insert to bring the I.D. back to size. My thoughts for you..the smaller Disco valve and stem, standard stroke, and a bit more spring pre-load. And if at all possible see if you can get the striker down to 50g or less. That will kill some of the dwell time.