DD 16” midlength gassing

[1168]

We all have our days.

After testing different carbine buffers with 5.56 ammo in an 11.5 AR upper with an adjustable gas block, I found the H2 has softer recoil than the lighter buffers. I also found that the carbine, H and H2 buffers required the same gas setting for full lock back. As it has been commonly accepted that heavier buffer weights required larger gas ports, this came as a complete surprise.

I read your testing on that, and thanks for posting it. In my own testing, where I attempted to reproduce yours (and I believe Buford T Justice), I concluded that my click (3 clicks/turn) adjustable gas block really wasn’t very fine, and more often than not, a setting that ran one buffer would run pretty much whatever buffer. Which of course mimics your results, just with a different conclusion. Which was that my results were inconclusive, and the heavier buffer smoothed out the not-really-all-that-fine-tuned setting.

I did find on my gamer gun that my recovery between shots was faster when tuned to run .223 with a buffer filled with aluminum weights.

I intend to do some experimenting with gas port inserts or EZ Tune tubes at some point, so I’ll have numbers. Maybe I’ll finally put that DD Mk 18 barrel to use.

[ta0117]

Several of the manufacturers you listed go smaller than .076" on a 16" bbl.

I checked the gas port spreadsheet and the manufacturers I listed all seem to go 0.076”. I feel like this is currently the “standard” for 16” midlengths since it gives reliable operation in all weather conditions.

Maybe my BCG has a better than usual gas seal as result of tolerance stacking. I think how gassy an rifle is depends on the individual rifle, even if all numbers on paper are the same because of production tolerances.

H2 and A5-2 seem to be the almost universal sweet spot.

Has 16” midlengths with H2 have any problems in cold weather? Wonder if this again depends on the individual even if all numbers on paper are the same.

[1168]

Has 16” midlengths with H2 have any problems in cold weather? Wonder if this again depends on the individual even if all numbers on paper are the same.

I’d be willing to bet 3 doughnuts that your rifle will run proper brass cased ammo with an H2 buffer, if thats what you’re asking. It’d probably also run the A5H2 that Mistwolf was getting on about, and you’d even feel a small difference with that.

However, this: https://www.primaryarms.com/strike-i...ensator-1-2x28 or this: https://www.primaryarms.com/surefire...comp556-1-2-28 would probably do more. But then your friend will hate you. Then you’ll want a silencer. And in 10 months, your rifle will be super overgassed. So you’ll be ****ing with buffers again. And then you’ll get a BRT EZ Tune. But then you’ll want a SBR. Its a disease. But the same $3,000 could buy enough ammo and training to kick your friend’s ass all over the range, also.

[lysander]

As it has been commonly accepted that heavier buffer weights required larger gas ports, this came as a complete surprise.

I assume sarcasm?

And, many 16" barrels are technically under-gassed, if you point them straight down and fire a single round they won't lock back on the empty magazine.

[17K]

Has 16” midlengths with H2 have any problems in cold weather? Wonder if this again depends on the individual even if all numbers on paper are the same.

There is nothing marginal about the gas drive with any 16” mid that I’m aware of.


All my midlength experience is with BCM and DD barrels.

The BCMs were complete uppers and cycled hard enough that they dented brass and beat up firing pin retainer pins. I ran those uppers up to A5-4 and they just seemed to recoil harder as the weight went up.

The DD barrels were rebuilds on Colt uppers, used new bolts and original carriers and were fine. I only ran them on A5-2 buffers.

[Disciple]

And, many 16" barrels are technically under-gassed, if you point them straight down and fire a single round they won't lock back on the empty magazine.

Is it safe to shoot into dirt to perform that test?

[opngrnd]

I assume sarcasm?

And, many 16" barrels are technically under-gassed, if you point them straight down and fire a single round they won't lock back on the empty magazine.

I've never heard of this test before. It certainly has my curiosity.

[MistWolf]

I assume sarcasm?

Years ago, when I first started seriously looking into the technical side of ARs, the common advice to fix an over gassed AR was to use a heavier buffer. Another bit of common advice was to use the heaviest buffer that still allowed full function. So, I figured a heavier buffer would require a larger diameter gas port. To my surprise, that turned out to be a false assumption.

…Then you’ll want a silencer. And in 10 months, your rifle will be super overgassed. So you’ll be ****ing with buffers again.

Not if you know what you’re doing. Instead of messing around with buffers,

you’ll get a BRT EZ Tune.

Or a BRT suppressor barrel.

But then you’ll want a SBR. Its a disease. But the same $3,000 could buy enough ammo and training to kick your friend’s ass all over the range, also.

Just get the SBR, suppressor AND training. It’s where you’re gone end up anyway.

[prepare]

11.5" Carbine .071
14.5" Carbine .0625
16" Carbine .0625
16" Mid .076

Combined with A5H2 offers a wide performance envelope; unsurpassed or suppressed, dirty, dry, hot, cold.

Not the end all be all but proven, reliable, and predictable.

[lysander]

Years ago, when I first started seriously looking into the technical side of ARs, the common advice to fix an over gassed AR was to use a heavier buffer. Another bit of common advice was to use the heaviest buffer that still allowed full function. So, I figured a heavier buffer would require a larger diameter gas port. To my surprise, that turned out to be a false assumption.

I think that is mostly due to the fact most people don't think about what is actually going on from a physics point of view. If you have an over-sized gas port, you are introducing more energy into the system than required. A heavy buffer does not remove energy from the system, it just slows the bolt's acceleration and to a lesser extent, the final velocity, But the excess energy is still there.

Let's say the amount of energy is E

1/2 x Mh x Vl^2 = E = 1/2 x Ml x Vh^2

with:

Mh = heavy mass
Ml = light mass
Vh = velocity, high
Vl = velocity, low

Since the velocity is squared, it will dominate the equations, the relatively small change in mass will not make large changes in bolt velocity. Try putting a .5 kg mass at 6 m/s into the equation and see how much mass will be required to slow the velocity by 10%. (Hint, the answer is nearly 25%)

What a heavy buffer does is reduce the initial acceleration of the the bolt, which helps in keeping rims intact during extraction. So, if you are severely over gassed, heavier buffer may cure some of the symptoms, but the problem of excess energy is still there.