View Full Version : Gas Piston weight
So I keep hearing how short stroke and long stroke piston rifles are heavier than direct impingement ones, but how much heavier are they? How much weight do short stroke and long stroke pistons tend to add to a rifle? Like how much does the individual piston system weigh?
Gas piston ARs, like the HK416, usually use a heavier profile barrel to deal with heat better. Some also use a heavy handguard. That's where the extra weight comes from.
The actual gas system adds only a couple of ounces to weight.
I don't know why, but whenever you look at a manufacturer that offers basically the same gun in both piston and DI versions, the piston one almost always weighs about a pound more.
But I think a bigger aspect is you are putting weight out on the end where you feel it more. Or, more accurately speaking, moving the piston out from inside the bolt carrier forward to the gas block.
If you play golf or tennis think about it like adding weight to the end to increase swing weight.
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I’ve come to the conclusion Mistwolf has. It’s less the piston itself and more the other characteristics of the rifle. The LMT NZ reference rifle and Mars-L piston are almost identical in weight. Both are medium profile with a beefy monolithic rail. The LMT barrel sleeve/extension is also heavy.
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I don't look at it as the piston adding weight so much as the DI gas tube reduces parts and weight and simplifies operation (in the AR realm anyway).
My thought is... What if you could eliminate those moving parts and replace them with a stainless steel tube??? :eek:
I don't look at it as the piston adding weight so much as the DI gas tube reduces parts and weight and simplifies operation (in the AR realm anyway).
My thought is... What if you could eliminate those moving parts and replace them with a stainless steel tube??? :eek:
Thread drift here, but why not. Look at this in the reverse. What if we could remove 3 cheap, thin, steel rings and replace them with a sturdier piston? Not advocating for pistons, just tossing up the counter-argument.
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Gas piston ARs, like the HK416, usually use a heavier profile barrel to deal with heat better. Some also use a heavy handguard. That's where the extra weight comes from.
The actual gas system adds only a couple of ounces to weight.
This is exactly the answer I was about to post. I have a bunch of Sig 516's, and like the HK 416, they are built like tanks. Lightweight construction was not a consideration for these types of rifles. they are designed for extreme heavy duty use. I do have a Centurion Arms 14.5 P&W that has a heavy barrel and a 12" pictany rail. It is virtually as heavy as my 516's. Most piston guns are simply built to a heavy duty use standard.
Piston rings are not a liability.
They are a more advanced design.
All of the better piston guns FN/HK/Steyr also use piston rings.
This is actually a credit to the design efficiency of the "DI" AR.
https://www.midwestgunworks.com/mm5/graphics/00000001/F141200010.jpg
https://mk0hkpartsnetky850kq.kinstacdn.com/wp-content/uploads/2019/08/gas-piston-complete-hk-mr556-416-g36-sl8-1.jpg
https://lh3.googleusercontent.com/proxy/xNe1xggcOM8FgE_FSuFrVMlaPQ_1U9xMKnMhYSCQYGC-8eqi1V2RNUEyCBNSeA4d2OxifCLN9nYXu2ISjGiEstd4aaJ04B1WlS_lJopZZKoOuhR9H8gmBa5lvk8P-Nk1uzlyY2F4Noixh7F-moXEjnycxvJ9x7i133Ghx-CGZOUdsGcUbk1Z85Bt6ulrwg
https://media.mwstatic.com/product-images/src/Primary/618/618233.jpg?imwidth=480
Look at this in the reverse.
What if we could remove 3 cheap, thin, steel rings and replace them with a sturdier piston?
Not advocating for pistons, just tossing up the counter-argument.
Piston rings are not a liability.
They are a more advanced design.
All of the better piston guns FN/HK/Steyr also use piston rings.
This is actually a credit to the design efficiency of the "DI" AR.
https://www.midwestgunworks.com/mm5/graphics/00000001/F141200010.jpg
https://mk0hkpartsnetky850kq.kinstacdn.com/wp-content/uploads/2019/08/gas-piston-complete-hk-mr556-416-g36-sl8-1.jpg
https://lh3.googleusercontent.com/proxy/xNe1xggcOM8FgE_FSuFrVMlaPQ_1U9xMKnMhYSCQYGC-8eqi1V2RNUEyCBNSeA4d2OxifCLN9nYXu2ISjGiEstd4aaJ04B1WlS_lJopZZKoOuhR9H8gmBa5lvk8P-Nk1uzlyY2F4Noixh7F-moXEjnycxvJ9x7i133Ghx-CGZOUdsGcUbk1Z85Bt6ulrwg
https://media.mwstatic.com/product-images/src/Primary/618/618233.jpg?imwidth=480
So why don’t older designs need them? Honest question, not trying to be contrarian.
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So why don’t older designs need them? Honest question, not trying to be contrarian.
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Older piston designs usually used a labyrinth seal characterized by groove rings. This is a very effective seal, however it requires length in order to work properly. Sealing rings allow for shorter seal distance. Note the length of the pistons shown above compared the the M14 piston.
https://www.fulton-armory.com/images/products/detail/FAGasPiston.jpg
Some designs just allowed for leakage and over sized the gas port.
The_War_Wagon
02-17-21, 21:17
With a loaded mag, this baby (POF-415 Gen.III) tipped the scales @ almost 11lbs, in 2009. :eek:
https://i.ibb.co/XDgL1dr/POF15.jpg
That's why my current HD rifle, weighs just under 7lbs - loaded. :cool:
https://i.ibb.co/6b1GyKx/100-5516-crop.jpg
Piston rifle was fun, it was different, it was cool, it got a lot of attention... and it damn near killed me at a couple of carbine classes :eek:
I'm 12 years older, & slower now. The main thing a piston rifle taught me was - get a LIGHTER rifle!!!
FWIW, I have a PWS Mk116 Mod 2 that weighs 6 lbs 8 oz naked. Has a tapered medium profile barrel and the long stroke gas piston. Even has a 15" handguard. Pretty light for a piston AR.
Thanks for the piston info. Back on topic. Let’s put the piston into context with actual data:
A midlength gas tube weighs 0.8 oz.
An LMT piston (regulator, piston, and spring) weighs 3.4 oz.
A difference of 2.6 oz.
A full rifle weighing 112 oz (7lbs), the difference in weight amounts to around 2%.
For reference:
BCM shorty MLok grip - 1.9 oz (~1.5%)
Difference between medium contour and light weight barrel (from BCM) - 6 oz (~5%)
Difference between LMT sopmod stock and BCM gunfighter stock - 4 oz (~3.5%)
In conclusion: The use of a piston systems weight penalty is in line with most other common AR accessories and build choices. It isn’t excessively heavy when put into perspective. Are the benefits worth the weight? That’s a question I can’t answer.
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The differences in weight should also include the gas block.
Piston gas blocks tend to be the heavier.
The standard FSB is pretty heavy at 4.8 oz.
A low profile DI gas block is pretty light at 1.4 oz.
The differences in weight should also include the gas block.
Piston gas blocks tend to be heavier.
The standard FSB is pretty heavy too, but low profile DI gas blocks are light.
Good discussion. I’ve never delved into piston weight before.
True, but I don’t have any to weigh. I only have piston experience in 5.56 with LMT. I can’t imagine between an LMT and fixed FSB being significant since piston gas blocks are bored out for the piston and regulator. A low profile I would suspect would be maybe an 1-2 oz lighter. Basically the difference between a fixed and low profile, which I never see brought up in weight discussions. Piston carriers will be slightly lighter too because of the lack of gas key and screws.
Real world comparison:
A Colt 6920 OEM-2 with LPVO, 13” BCM MCMR rail, etc etc weighs 9 lbs 5 oz. unloaded.
An LMT MRP piston set-up similarly but with a 1 oz heavier stock, 1 oz heavier scope, and 1 oz heavier light mount weighs 10 lbs exactly.
So 11 oz difference between the rifles that isn’t accounted for in accessories. In DI, LMT MRP barrel is 2.3 lbs, gov profile Colt is 2 lbs both with FSB. That accounts for 4.8 oz in barrel profile.
So overall, it appears the piston is adding a bit over 1/4 lb (4 oz). That’s not insignificant, but it isn’t making the piston a boat anchor like a lot of people seem to believe.
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sasquatchoslav
02-19-21, 04:52
FWIW, I have a PWS Mk116 Mod 2 that weighs 6 lbs 8 oz naked. Has a tapered medium profile barrel and the long stroke gas piston. Even has a 15" handguard. Pretty light for a piston AR.
I run the MK111 in 7.62x39 crazy light enough for me.
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