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cold co2 rifle barrel

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Ffisher

Member
Mar 1, 2023
17
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ALLENTOWN
I observed something today and my brain put 2 n 2 together. First of all I shoot in my basement. I always notice that my Diana Chaser rifle barrel is cold after going through a couple of co2 cartridges. But today I noticed what clicked in my head. I set up 4 targets and had 4 mags with 7 pellets in each, 7 shots for each target. 1st target had a nice group, 2nd target group was a little bigger, 3rd target bigger and 4th target even bigger. Now what I realized was the colder the barrel got the wider the group.
My question is, is there anything I can do to prevent the barrel from getting cold ? Would a shroud around the barrel help?
Bill
 
First and foremost, make sure it's not wasting CO2. Many times that's the biggest contributor to getting cold and losing velocity.

Do you have a chronograph? If so, run a full string and total up the energy. If it's producing less than 300fpe or so, there's room for improvement by either shortening the hammer spring or by adding an O-ring buffer for the hammer (aka bstaley O-ring buffer).
 
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Shroud around barrel will not help as any insulating effect realized will just help keep the barrel cold. The cooling of the barrel is from the expanding co2 inside the barrel.

Co2 cools as it expands, the more you shoot the colder it gets. As cold as the barrel is the co2 cartridge is even more so. The colder it gets the more the pressure drops and the slower the pellet is propelled. Nature of the beast.

Shorter shooting strings and/or more time between shots can help, giving co2 cartridge time to warm a bit or at least slow rate of cooling.
 
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Ffisher said:
I have a cheap chrony and am getting about 485 fps for the first 2 or 3 shots then it goes down from there. I'm using a stronger hammer spring with a 1/4" spacer. Not sure what the velocity is. I'm getting about 25 good shots per co2 cartridge before it starts loosing power.
Bill
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485fps so I'm assuming .22 cal. What weight pellet?

FWIW, it's almost never helpful to swap to a heavier hammer spring in a CO2 gun unless the valve throat has been enlarged. Most guns are already wasteful of CO2 in OEM form, in which case a heavier hammer spring succeeds in making it louder, not faster, because it's belching CO2 after the pellet has left the barrel. Not saying that's the case here, just that most CO2 guns are oversprung from the factory.
 
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.22 cal. 14.0gr wadcutter. My gun seems to like wadcutter pellets, more accurate, any brand, I use RWS and H&N brand mostly. I get fair results with domed pellets. Weight between 14.0 and 14.6gr. With the heavier hammer spring, I was going by what several people claim on youtube to increase fps. I do realize that youtub info isn't always true. I did find out that after several hundred shots I have to retighten the screw that holds the valve in place and the hammer screw. tomorrow I will put the original hammer spring in and recheck the fps. If I recall correctly ,before the mod the fps was somewhere around 450 fps.
Bill
 
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