Anyone with a gas ram and chrono, help please to solve a mystery!!

[Loki_79]

If you have any gas ram powered rifle and also access to a chronograph, could you please help me out by recording the fps (or power) of two consecutive shots.

1) Where the rifle is cocked as fast as you can - probably your 'normal' cocking action
2) Where the rifle is cocked as slowly as you can - try to go as slow as possible, this may be difficult with shorter barrels

The order does not matter. Please post the results on this thread.

I have good reason to believe that there should be a marked difference between the two, but hopefully all will become clear (one way or another) when a few results come in. Thanks in advance!!

[angrybear]

I don't have a gas ram, but I don't believe it should make any difference to it, being a sealed unit.

it would if you made multiple shots as fast as possible as the gas would heat up but that's a different matter.

[Loki_79]

Yes, you would certainly think so - but a certain forum member has been testing one where the difference is significant and I would like to find out if this is the exception or the rule!

I don't have a gas ram, but I don't believe it should make any difference to it, being a sealed unit.

it would if you made multiple shots as fast as possible as the gas would heat up but that's a different matter.

[thisisdonald]

I have noticed that with SSP pistols, you can cock hard, or soft and it definintely feels like the stroke is harder if you cock fast and hard.




that sounds all kinds of wrong

[TonyL]

Yes, you would certainly think so - but a certain forum member has been testing one where the difference is significant and I would like to find out if this is the exception or the rule!

I'd guess that if the rifle was shot very quickly, immediately after the faster / harder cocking action, then the higher temperature generated would increase the pressure inside the ram? If, however, the rifle was allowed a little "standing time" and that higher temperature dissipates, then it would be the same?

Also, higher ram pressure may not ALWAYS lead to higher muzzle velocities, a little like if a springer is oversprung?

[flyingfish]

I'd guess that if the rifle was shot very quickly, immediately after the faster / harder cocking action, then the higher temperature generated would increase the pressure inside the ram? If, however, the rifle was allowed a little "standing time" and that higher temperature dissipates, then it would be the same?

Also, higher ram pressure may not ALWAYS lead to higher muzzle velocities, a little like if a springer is oversprung?

I thought the use of inert gas was supposed to stop that happening yony

Pete

[severnsider]

I've mentioned this phenomenon several times on here in recent years. Slow cock gives lesser m.v. Than fast cock. It's a mystery to me. As BTDT pointed out, the air we breathe is 78% nitrogen so there's not much of an argument for filling with inert gas. Another member (Blackbeard) gave the matter some thought too. Loki, what has prompted you to raise the matter again?

[flyingfish]

just put my anorak on and found that according to the "Ideal Gas Law" a temperature change of 10f brings about a pressure change of 1.9%

Pete

[Phil Russell]

I've mentioned this phenomenon several times on here in recent years. Slow cock gives lesser m.v. Than fast cock. It's a mystery to me. As BTDT pointed out, the air we breathe is 78% nitrogen so there's not much of an argument for filling with inert gas. Another member (Blackbeard) gave the matter some thought too. Loki, what has prompted you to raise the matter again?

Yes, I was sure the issue has been discussed before .. maybe a couple of years ago (?). I think the conclusion was that there can be a difference and that to get consistency in mv you need consistency in cocking action. But I am not certain that the differences were that pronounced as to create worry.

Cheers, Phil

[Loki_79]

I've mentioned this phenomenon several times on here in recent years. Slow cock gives lesser m.v. Than fast cock. It's a mystery to me. As BTDT pointed out, the air we breathe is 78% nitrogen so there's not much of an argument for filling with inert gas. Another member (Blackbeard) gave the matter some thought too. Loki, what has prompted you to raise the matter again?

Have you got any numbers to quantify the difference? And how 'slow' is the slow cocking stroke? 5 seconds, 10 seconds? I have been presented with some data that appears to break the laws of thermodynamics, so I wanted to get a wider sample of data before we have to re-write all the physics books!

[severnsider]

Have you got any numbers to quantify the difference? And how 'slow' is the slow cocking stroke? 5 seconds, 10 seconds? I have been presented with some data that appears to break the laws of thermodynamics, so I wanted to get a wider sample of data before we have to re-write all the physics books!

When (if) it stops raining I will gather fresh data from four gas rams of differing calibres and barrel lengths and post them here for you. 5 shots 'slow' cock (5s) and 5 shots 'quick' cock (1s). How does that sound? I'll do it if you agree to share your theory on why it happens when you see the data. OK?

[buttloaves]

This was discussed a few weeks back, i suggested the power output would go up (in the case of a gas ram) if it was cocked and fired quickly due to the gas heating up on compression, a lot of people doubted it would have any effect, JT did a quick test and found the power went up by 70fps, enough to push a gun over the limit, and that was a nitro ram i think.

[buttloaves]

Gut feeling says yes, especially as you've got 76% nitrogen in there already, Mike.

Having said which, I did a test yonks ago on a nitro piston gun, and the velocities were practically identical with it acclimatised to 16C and 34C, so you never know unless you try.

OK, scratch that. I've just tested quick Vs. slow cocking with the nitrogen filled ram rifle and the difference is 70 fps

That's 11.4 ft. lb. fast, 9 ft. lb. slow.

^^ this

[Loki_79]

When (if) it stops raining I will gather fresh data from four gas rams of differing calibres and barrel lengths and post them here for you. 5 shots 'slow' cock (5s) and 5 shots 'quick' cock (1s). How does that sound? I'll do it if you agree to share your theory on why it happens when you see the data. OK?

Definitely a deal! That sounds perfect, thanks for your help. I used to have an Evo, but I've since sold it, so can't try this myself.

I'm happy to share my theory now, but I would rather get some data first so as not to bias any measurements.

[severnsider]

Definitely a deal! That sounds perfect, thanks for your help. I used to have an Evo, but I've since sold it, so can't try this myself.

I'm happy to share my theory now, but I would rather get some data first so as not to bias any measurements.

Have a look here Sir http://www.dursley.org.uk/air/Cockingtests.pdf

I think you'll find it all rather inconclusive, apart from the undeniable fact that, on average, a quick cock gives slightly more m.v. in all cases. Pellets all JSB Exacts, straight from the tin. Chrony F1, 6" from muzzle. The longer barrels seem "better" than the shorties.

Some rifles more consistent with a slow cock. Would be interested in what you make of it!

As Phil Russell said earlier, none of this makes a great deal of difference to the pellet hitting the target.

Good luck with your research