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

[severnsider]

^^ this

How do you find all these old posts? I always seem to lose track of them!!!!!!

Posted this mornings findings here http://www.dursley.org.uk/air/Cockingtests.pdf but couldn't achieve anything like Jim's 70fps difference.

[air-tech]

Wonder whether the only variable is speed of cocking, or whether as a part of this, comes speed of shooting (after cocking).

Purely hypothesising here, any cocking action will increase the temp of the gas (hence pressure) in the ram. This heat will eventually dissipate. So if from *start* of cock to pulling the trigger, one takes 15 seconds as opposed to 45 seconds, then there could be an explanation there.

Similarly, with a slow cock, while the rise in heat energy (not necessarily rise in temperature of the gas... as will be made clear) will be identical as with a fast cock, during the slow cocking cycle heat has time to be dissipated to a larger surface area of the (un/partially compressed) gas ram cylinder, whereas with a fast cock there is barely any time and the heat must mostly be dissipated at the end of the cocking stroke, over the shorter length of the cylinder where the compressed gas now resides, so ultimately the temperature here will be higher and stay so for longer.

But if one were to let the gun cool down for a length of time that eliminates all this - say, 10 minutes - so the ram gas temps are near identical - do we see the same variable results? If not, mystery solved.

[Shed tuner]

good hypothesis

[angrybear]

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?

I suppose in theory if you "slam" the lever the sudden force might expand the skirt of the ram piston to make a tighter seal where with a slow gentle push the skirt would not be forced as tight allowing some gas to escape around the seal, which in turn would act as a cushion the wrong side of the ram piston.

[severnsider]

Wonder whether the only variable is speed of cocking, or whether as a part of this, comes speed of shooting (after cocking).

Purely hypothesising here, any cocking action will increase the temp of the gas (hence pressure) in the ram. This heat will eventually dissipate. So if from *start* of cock to pulling the trigger, one takes 15 seconds as opposed to 45 seconds, then there could be an explanation there.

Similarly, with a slow cock, while the rise in heat energy (not necessarily rise in temperature of the gas... as will be made clear) will be identical as with a fast cock, during the slow cocking cycle heat has time to be dissipated to a larger surface area of the (un/partially compressed) gas ram cylinder, whereas with a fast cock there is barely any time and the heat must mostly be dissipated at the end of the cocking stroke, over the shorter length of the cylinder where the compressed gas now resides, so ultimately the temperature here will be higher and stay so for longer.

But if one were to let the gun cool down for a length of time that eliminates all this - say, 10 minutes - so the ram gas temps are near identical - do we see the same variable results? If not, mystery solved.

Possible I suppose. For each shot I put in a pellet, cocked and shot straight after cocking so there should be little inconsistency between cocking and shooting. Slow cock was in excess of 20s each time and probably about 3 or 4s between cocking and firing.

[Loki_79]

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

Thank you very much for your time and effort. These results are nowhere near as dramatic as the other report which originally prompted the thread, suggesting that (as with everything it seems) nothing is ever simple.

As others have mentioned, thermodynamics tells us that given enough time for gas temperature to equalise with the rifle (a big metal heat sink) any cocking speed should give the same ram pressure. Indeed waiting for some time (could calculate this from the ram surface area and thermal transfer coefficient), should produce identical results for both.

It seems like further experimentation is required with individual parts of the offending rifle to identify the cause!

[buttloaves]

Thank you very much for your time and effort. These results are nowhere near as dramatic as the other report which originally prompted the thread, suggesting that (as with everything it seems) nothing is ever simple.

As others have mentioned, thermodynamics tells us that given enough time for gas temperature to equalise with the rifle (a big metal heat sink) any cocking speed should give the same ram pressure. Indeed waiting for some time (could calculate this from the ram surface area and thermal transfer coefficient), should produce identical results for both.

It seems like further experimentation is required with individual parts of the offending rifle to identify the cause!

Fit a pressure gauge to the ram and see how cocking speed affects it.

[severnsider]

Fit a pressure gauge to the ram and see how cocking speed affects it.

Nice idea....... some kind of adapter via the Schrader port?

[severnsider]

Thank you very much for your time and effort. These results are nowhere near as dramatic as the other report which originally prompted the thread, suggesting that (as with everything it seems) nothing is ever simple.

As others have mentioned, thermodynamics tells us that given enough time for gas temperature to equalise with the rifle (a big metal heat sink) any cocking speed should give the same ram pressure. Indeed waiting for some time (could calculate this from the ram surface area and thermal transfer coefficient), should produce identical results for both.

It seems like further experimentation is required with individual parts of the offending rifle to identify the cause!

Now then, here is some further data which will get you scratching your head. I left an old Taunus cocked (slow cock) over night.
Just shot it over the chrono after 22 hours in the cocked condition: 661fps

A few "quick cocks" gave 671, 669 - around 8-10 fps gain over the "rested" condition;

A "slow cock" gave 554 - less than the "slow cocked and rested".

So what do you conclude? Indicative of internal leaks perhaps? Hope you find this of use Loki_79

[elewis411]

I once did some chronograph testing with my brand new .177 evolution and found if you cock and fire shots quickly the fps would steadily drop by around 10 fps each time until I got to around 700 fps. I couldn't get a difference between cocking fast or slow though.

[air-tech]

Now then, here is some further data which will get you scratching your head. I left an old Taunus cocked (slow cock) over night.
Just shot it over the chrono after 22 hours in the cocked condition: 661fps

A few "quick cocks" gave 671, 669 - around 8-10 fps gain over the "rested" condition;

A "slow cock" gave 554 - less than the "slow cocked and rested".

So what do you conclude? Indicative of internal leaks perhaps? Hope you find this of use Loki_79

Sample size too small, methodology faulty

There are other variables, which need to be eliminated to ensure that you are only getting results for what you want to test for. Such as the effect of lube, which effect varies when a gun is left standing or otherwise. It's a "springer" in all but power source.

I would - Time start of cocking, cock fast, let it sit for 10 minutes from start of cocking time. Shoot. Do this ideally 10 times, and chrono (yes... I know...)

Repeat above, always 10 minutes from start of cocking, but this time cock slowly, try to make it last 10 seconds just to make it reallll slowwww...

Ideally however... to eliminate other variables such as time of day, air temp, humidity, and more importantly the possibility of repeated shooting changing lube characteristics, etc - alternate a fast and slow cock.

Many thanks in advance for your efforts, let us know tomorrow

[severnsider]

Sample size too small, methodology faulty

There are other variables, which need to be eliminated to ensure that you are only getting results for what you want to test for. Such as the effect of lube, which effect varies when a gun is left standing or otherwise. It's a "springer" in all but power source.

I would - Time start of cocking, cock fast, let it sit for 10 minutes from start of cocking time. Shoot. Do this ideally 10 times, and chrono (yes... I know...)

Repeat above, always 10 minutes from start of cocking, but this time cock slowly, try to make it last 10 seconds just to make it reallll slowwww...

Ideally however... to eliminate other variables such as time of day, air temp, humidity, and more importantly the possibility of repeated shooting changing lube characteristics, etc - alternate a fast and slow cock.

Many thanks in advance for your efforts, let us know tomorrow

I'm not testing for anything at all! Just doing something that another forum member asked me to try. I'm done with it all now. My four rammers shoot fine whatever is going on inside. Someone else can ponce about if they want to - I've had enough!!!!

[TonyL]

Posted this mornings findings here http://www.dursley.org.uk/air/Cockingtests.pdf but couldn't achieve anything like Jim's 70fps difference.

Huge difference with the short barrel, low power .177 though, Mike.

Endorsement of that old saying going along the lines of, "If you've only got a little one, best do it fast!"

[severnsider]

Huge difference with the short barrel, low power .177 though, Mike.

Endorsement of that old saying going along the lines of, "If you've only got a little one, best do it fast!"

Ooooooh Matron! Yes, I've pumped it back up to the "proper" power level now. I'll be having another go at the bucket with it next month!

[lensman57]

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

I have this with my HW 40. The difference is not a lot but is there. Now HW 40 only makes 2.6 ft.lbs at the muzzle at best so 0.3 ft.lbs differential is significant. I'd be interested to see what the result of the rifles would be.

A.G