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sonofsammo

Joule creep and then some...

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I was tinkering with my SRS and swapped out the spring. And came up with some interesting results on the chrono.
The results were somewhat disturbing. somewhere between 30 and 40% increase in power, just by changing the ammo. Literally nothing else was changed.
But then, the power went UP again when I put the hop on, which really surprised me. And disturbed me. Because at that point it became an air rifle (afaik). So out came the spring. Which was sad, because she was shooting beautifully!
I can't believe that there are places that chrono on 0.2s. It means there are people out there who could be unintentionally running seriously hot rifles. It also means there are some people out there intentionally running seriously hot rifles. 
Someone commented on FB yesterday about a big National game coming up and said they chrono on .2's - they called it the national air rifle competition... Scares the shit out of me...
Anyway, back to the drawing board for me!

 

Screenshot 2019-08-21 at 08.09.25.png

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When the hop is turned up the air seal improves on my bolty! Which doesn't help on top of the joule creep!

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this is the reason i always try and chrono on the ammo i'm using, because the differences can be really profound with the right setup.

 

i'm surprised you're getting that much out of a spring gun, heavy piston i'm guessing? i'd expect that much out of a gas gun or hpa under the right conditions.

 

unfortunately the whole chrono'ing on .2's is still pretty common, i've had plenty of instances where running the heavies i've been told "it's a bit low isn't it?" when i've told them the weight i'm running, they've set the chrono to that weight, and the joule reading is bang on the limit. kinda scary how easy it would be to just play ignorant, turn it up and run hot, but then i wouldn't be able to whine about other people running hot if i did that.

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47 minutes ago, Adolf Hamster said:

this is the reason i always try and chrono on the ammo i'm using, because the differences can be really profound with the right setup.

 

i'm surprised you're getting that much out of a spring gun, heavy piston i'm guessing? i'd expect that much out of a gas gun or hpa under the right conditions.

 

unfortunately the whole chrono'ing on .2's is still pretty common, i've had plenty of instances where running the heavies i've been told "it's a bit low isn't it?" when i've told them the weight i'm running, they've set the chrono to that weight, and the joule reading is bang on the limit. kinda scary how easy it would be to just play ignorant, turn it up and run hot, but then i wouldn't be able to whine about other people running hot if i did that.

Yup it's a heavy piston. Could easily get it higher too!

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I recently installed a ASP trigger set with their m150 spring, says it should be around 500fps, i know they are notorious for underrating their springs but it was shooting 570 fps on .2s

 

Swapped to .43 ammo, was shooting 432fps at 3.7 joules!

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1 hour ago, Adolf Hamster said:

this is the reason i always try and chrono on the ammo i'm using, because the differences can be really profound with the right setup.

 

i'm surprised you're getting that much out of a spring gun, heavy piston i'm guessing? i'd expect that much out of a gas gun or hpa under the right conditions.

 

unfortunately the whole chrono'ing on .2's is still pretty common, i've had plenty of instances where running the heavies i've been told "it's a bit low isn't it?" when i've told them the weight i'm running, they've set the chrono to that weight, and the joule reading is bang on the limit. kinda scary how easy it would be to just play ignorant, turn it up and run hot, but then i wouldn't be able to whine about other people running hot if i did that.

Same here, I  chrono my HPA rifs at home with .2 and .32 bb's for joules not fps to ensure I meet the legal requirements first and then the site requirements. 

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Oof, that's eye opening.  And one in the eye to the "only gas / HPA guns creep significantly" brigade.

 

Truth to tell, I've never cronoed my boltie on anything other than 0.2g, where it comes in at just under 500fps when hopped for 0.43g. That's what the local site lists their limit in, rather than in Joules, and I agree, it's wrong and probably actionably negligent, but what else am I meant to do?  Insist on chronoing with 0.43g despite their site rules?

 

That said, the tools of the State could drop an 0.86g steel BB in there, chrono it at over 2.5J and do me for having an unlicensed air rifle (Scotchlaw).  So, do I test with some of those and probably mess my hop rubber?

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35 minutes ago, Rogerborg said:

Oof, that's eye opening.  And one in the eye to the "only gas / HPA guns creep significantly" brigade.

 

Truth to tell, I've never cronoed my boltie on anything other than 0.2g, where it comes in at just under 500fps when hopped for 0.43g. That's what the local site lists their limit in, rather than in Joules, and I agree, it's wrong and probably actionably negligent, but what else am I meant to do?  Insist on chronoing with 0.43g despite their site rules?

 

That said, the tools of the State could drop an 0.86g steel BB in there, chrono it at over 2.5J and do me for having an unlicensed air rifle (Scotchlaw).  So, do I test with some of those and probably mess my hop rubber?

If it's running just under 500 on .2's I think you can say with 99.9% certainty you'll be over the 2.5J.
I chrono at home for the weight I'm going to play with and the limit of 2.32J, which is the equivalent FPS for 500 fps on a 0.2. That way I know I'm not cheating. Pisses me off that I know I'm playing against people who will either by accident or design be running hot rifles, but at least I know I'm playing fair.
I think any site that only chrono's on 0.2 should themselves having a hard time in the case of injury from a hot rifle. Although, I'm not sure which law they'll fall foul of tbh, so they may just get off scot free.
 

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What length inner barrel do you have?

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1 hour ago, Rogerborg said:

Oof, that's eye opening.  And one in the eye to the "only gas / HPA guns creep significantly" brigade.

 

yeah, it's not so much an issue for aeg's at least, because a heavier piston on an aeg is counter to people's normal desire to maximise rof without getting pme.

 

the thing is is that with this sort of thing people can be doing it unknowingly, people will hear "run a heavy piston and use heavy ammo, it'll help your range" without picking up on exactly why, and if their local site is doing the ol' .2's then they can be doing this without even realising that's what's actually happening.

 

sadly the poor sod on the recieving end isn't going to have the luxury of such ignorance.

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16 minutes ago, Wo1f said:

What length inner barrel do you have?

Me? It's the 20 inch sport, so 520 I think..

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1 hour ago, sonofsammo said:

I chrono at home for the weight I'm going to play with and the limit of 2.32J, which is the equivalent FPS for 500 fps on a 0.2. That way I know I'm not cheating.

 

If the site specifies a Joule limit, which sadly few seem to do.

 

If they say 500fps on 0.2g, and that's what they test to, then you're not cheating if you tune to that, you're complying.

 

The safety and legality issues are important but separate arguments.

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1 hour ago, sonofsammo said:

Me? It's the 20 inch sport, so 520 I think..

Have you repeated the test with a standard/light bolt? You might find your .20 FPS climbs but your .45 joules drop

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1 hour ago, Rogerborg said:

If they say 500fps on 0.2g, and that's what they test to, then you're not cheating if you tune to that, you're complying.

 

in a technical sense, although its better to take the spirit of the test rather than it's actual statement.

 

x fps on y weight is just a misleading way of quoting a joule figure anyway.

 

fortunately here it's easy- flat 1j limit so no messing around worrying what a given site's limit is going to be.

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Spring guns usually have high cylinder volume. That paired with heavy piston causes huge joule creep with heavy BBs.

VSR buckings designed to work only with hop on. The contact patch holds the BB in place until the pressure builds high enough so you will have higher FPS with hop on. If you have no hop at all, the BB just rolls out of the barrel after charging the gun.

AEG buckings hold the BB in place in front of them with their lips. Those will have less fps with hop on because the hop slows the BB a bit.

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On 21/08/2019 at 11:39, sonofsammo said:

If it's running just under 500 on .2's I think you can say with 99.9% certainty you'll be over the 2.5J.

 

I've seen negative joule creep in my springer and all my AEGs so I'd actually bet the other way. 

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46 minutes ago, Lollingsgrad said:

 

I've seen negative joule creep in my springer and all my AEGs so I'd actually bet the other way. 

Negative joule creep in what sort of springer?
And what did you change that made it happen?

 

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VSR, and both stock and after fiddling. I suspect joule creep is something you normally need to tune to get (i.e. Weighted/heavy piston) but I've not tried myself. 

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