Testing Buffer Weights and Gas Flow

[MistWolf]

Last weekend, I loaded up my two suppressed shorty ARs in my Jeep and drove out to the desert to test them with different buffer weights. I wanted to see just how much changing a buffer actually affected function and felt recoil.

The first shorty is a pistol I nicknamed the "Wolf Pup". I built it shortly after Sig introduced it's arm brace. It's evolved some since it's first inception, but as it sits now, it has a 11.5" barrel, suppressor, standard full auto BCG and an SLR adjustable gas block. The lower uses a pistol receiver extension and at the start of this test, an H buffer & carbine action spring.

The SLR upper was tuned using the lock back check. It was tuned until the round would eject, but not lock back. Opening the gas port one more click resulted in full ejection and lock back. To my surprise, no change to the gas port setting was needed with the different buffer weights. What did change, was felt recoil. While recoil with all three buffers was never unpleasant, recoil with the carbine buffer felt quicker and sharper than with the heavier buffers. Of the three buffers, recoil felt softest and flattest with the H2 buffer

Next, the SLR upper was tried on a lower with the A5H2 buffer and Sprinco green action spring. Again a lock back check was performed. Again, no change was made to the gas port setting. Recoil felt even softer and flatter than with the H2 buffer. Oddly, the carrier speed felt slower, almost sluggish when fired at a deliberate pace. However, that sluggish feeling went away during rapid fire.

I was surprised that no change was needed to the gas port setting when switching even from the lightest buffer to the heaviest. What was really interesting is that the AR shot the softest and flattest with the A5 RE assembly. The conclusion I draw from this test is that taming an over-gassed AR will take more than heavier buffers and stiffer springs. It also takes getting the gas flow.

 

[Varminterror]

I've said it many times... a heavier buffer is a bandaid fix for the wrong problem - aspirin for a brain tumor. Regulate your gas!

 

[wally]

The only real point of a heavier buffer is to reduce the bolt velocity. This is usually necessary with 9mm and other "blowback" AR calibers. In theory it might help with the barrel gas blowback fouling when shooting suppressed, but in my experience its a minimal reduction.

The "softer shooting" aspect of it is subjective, do it if you like it, but I tend to assume if a heavier buffer really had merit the designers would have used them. People fire a relatively small number of rounds under very benign conditions (pleasant day at the range) and declare them "beneficial" based on some subjective criterion.

 

[MistWolf]

What do you consider a "heavier buffer"?

 

[wally]

What do you consider a "heavier buffer"?

Ones that weighs more than the 5.56 standard buffer. For carbines they are usually marked H, H1, H2, etc.

"Standard" is something line 3.0 oz for a carbine, 5.1 oz for a rifle, H1 is typically 3.7 oz, 9mm buffers are usually about 5.5 oz

 

[Driftertank]

I tend to think that heavier buffers aren't so much for taming recoil as improving reliability....the same amount of kinetic energy is imparted for a given gas flow, whether it is light or heavy. But the same momentum, imparted on a heavier buffer, will impart less speed (energy = mass × velocity^2). This means the heavy buffer will allow more time for things like magazine and ejector springs to function. I feel like a heavier reciprocating assembly (BCG+buffer) will tend to show less function change as gas port pressures/sizes change, because it takes longer for the assembly to move as pressures build in the bolt, so port flow has less effect on gas volume in the bcg (does that make sense?) up until the point that the bullet exits the muzzle and port pressure starts to drop.

If my understanding seems incorrect, I'm happy to be educated by someone with better understanding

 

[DeanV]

I have a 10.5” ar pistol that I want to swap between both 5.56 and a soon to arrive 9mm upper. The current buffer is a standard carbine H buffer. Is there one buffer set up that will work well for both? I know some people use a heavier buffer for short barrel ar's. The oroignal configuration is a stock PSA pistol with the sb tactical brace and 10.5” 5.56 barrel. The 9mm upper will be the stern defense 10.5” 9mm upper. Eventually I may add a can to the 9mm.

 

[wally]

My advice, would be to try the 9mm buffer with the 5.56 upper, if it works acceptably you are done, if not just swap buffers when you remove the mag block from the lower to change calibers.

I've not had a lot of luck with standard weight buffers in 9mm ARs -- the carrier velocity is too high and it can out run the magazine springs leading to "bolt-over-base" feed failures, aka nose up jams, as the bolt catches the extraction groove instead of the cartridge base. In extreme cases you can get it closing on an empty chamber which can be mis-diagnosed as "short stroking".

 

[MistWolf]

Ones that weighs more than the 5.56 standard buffer. For carbines they are usually marked H, H1, H2, etc.

"Standard" is something line 3.0 oz for a carbine, 5.1 oz for a rifle, H1 is typically 3.7 oz, 9mm buffers are usually about 5.5 oz

Just wondering. According to my notes, a carbine buffer weighs 3.0 oz. Colt sells their commercial 6920 with an H buffer (3.8 oz) and the full auto M4 with the H2 buffer (4.6 oz). Rifle buffers are 5.2 oz. Rifle buffers weigh 5.2 oz. The A5H2 buffer for the A5 RE weighs 5.3 oz.

The 3.8 oz H buffer is the standard for commercial buffers and the 4.6 oz the standard for military M4. The 3.0 oz carbine buffer is just too light.

I consider the H2, A5H2 and rifle buffers in the standard weight range, the H as the lightest acceptable weigh buffer and the carbine buffer too light when tuning an AR for the widest span of operation. Tuning an AR as a game gun is another subject.

 

[MistWolf]

I have a 10.5” ar pistol that I want to swap between both 5.56 and a soon to arrive 9mm upper. The current buffer is a standard carbine H buffer. Is there one buffer set up that will work well for both? I know some people use a heavier buffer for short barrel ar's. The oroignal configuration is a stock PSA pistol with the sb tactical brace and 10.5” 5.56 barrel. The 9mm upper will be the stern defense 10.5” 9mm upper. Eventually I may add a can to the 9mm.

I would use an H2 buffer for 5.56 and swap in a 9mm buffer when shooting your 9mm upper. Or use the VLTOR A5 pistol RE with the A5H2 buffer which weighs 5.3 oz and see if it will work for both.