CO2 pistol MV consistency

[badger5th]

I understand CO2 is temperature sensitive. The small amount of evaporation with each shot lowers the temp of the remaining CO2 which lowers the amount of boil off for the next shot.

Any guideline on how long to pause between shots to keep the MV at peak? Unless I'm misunderstanding something I understand as long as enough liquid remains under pressure to evaporate for a shot, the MV should not drop significantly over the service of the CO2 capsule assuming the temperature remains constant.

 

[nervoustrig]

Well, there are really too many variables involved to offer a useful answer. How much CO2 is exhausted per shot, temperature delta between the reservoir and ambient, thermal conductivity of the reservoir, state of tune, etc.

As a practical matter, I would say the most effective strategy is two-fold:

1. Balanced state of tune: Adjust the hammer spring tension to the velocity knee (95-97% of maximum velocity) just as you would a regulated PCP. In doing so, the gun is less sensitive to variations in pressure that arise from temperature changes.
2. Miserly use of CO2: In most cases, item 1 gets you a long way toward this goal because most CO2 guns in OEM form are extraordinarily wasteful of CO2. Way too much hammer strike, way too much CO2 blown out every time the trigger is pulled...thus the self-cooling effect is exaggerated. Simply reducing the hammer spring tension to the knee is a big improvement.
   
   To take it a step further, employ one of the popular air-saving techniques like a simple bstaley O-ring stack between the hammer and valve, or a free-flight hammer (SSG or SSS), and/or a lightweight hammer.

To give you some idea, I generally get over a 50% improvement in shot count using this approach. The benefits are numerous...quieter, not having to swap cartridges so often, and a more stable velocity.

 

[Steveoo]

The other issue is of course, ambient temperature effects…
Zero the gun on a cold morning, only to find it shooting high at a hot noon and a bit less on a moderately warm evening.
The original premise of zero recoil was so impacted by varying temps, and gun cool down that it got dropped from the Target pistol circuit a decade ago.
However, on a nice warm day, your little Crosman 150 with a few sight setting shots can be great fun….must dont be so quick reloading it as it will punish you.

 

[badger5th]

Well, there are really too many variables involved to offer a useful answer. How much CO2 is exhausted per shot, temperature delta between the reservoir and ambient, thermal conductivity of the reservoir, state of tune, etc.

As a practical matter, I would say the most effective strategy is two-fold:

1. Balanced state of tune: Adjust the hammer spring tension to the velocity knee (95-97% of maximum velocity) just as you would a regulated PCP. In doing so, the gun is less sensitive to variations in pressure that arise from temperature changes.
2. Miserly use of CO2: In most cases, item 1 gets you a long way toward this goal because most CO2 guns in OEM form are extraordinarily wasteful of CO2. Way too much hammer strike, way too much CO2 blown out every time the trigger is pulled...thus the self-cooling effect is exaggerated. Simply reducing the hammer spring tension to the knee is a big improvement.
   
   To take it a step further, employ one of the popular air-saving techniques like a simple bstaley O-ring stack between the hammer and valve, or a free-flight hammer (SSG or SSS), and/or a lightweight hammer.

To give you some idea, I generally get over a 50% improvement in shot count using this approach. The benefits are numerous...quieter, not having to swap cartridges so often, and a more stable velocity.

To the best of my knowledge the only readily adjustable CO2 gun I own is a Crosman 2240. I've had it apart before so it's no big deal. The others are replicas with blow back (wastes gas, I know). I don't care as much about MV drop with the replicas since I use those for more practical rapid fire practice. An adjustment on the 2240 would be something I'd be inclined to try. Thanks for the feedback.

 

[badger5th]

The other issue is of course, ambient temperature effects…
Zero the gun on a cold morning, only to find it shooting high at a hot noon and a bit less on a moderately warm evening.
The original premise of zero recoil was so impacted by varying temps, and gun cool down that it got dropped from the Target pistol circuit a decade ago.
However, on a nice warm day, your little Crosman 150 with a few sight setting shots can be great fun….must dont be so quick reloading it as it will punish you.

Thanks for the input. I never do anything at winter temps with CO2. Winter shooting for me is either on my basements range or on the range at New England Airguns. Both spaces heated to normal room temperature. regards.