Need 300BLK buffer help!

Guns & Gear Guns
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I had a couple problems when shooting 200 grain subsonic ammo. In a 20 round sample, one cartridge jammed between the bolt and the chamber (the spent casing ejected). The other problem was the bolt failed to lock back on an empty magazine (firing the last round).

I’ve been shooting 150 grain ammo in it with zero problems.

I just checked and I had a 5.6 ounce buffer (H3?) in it. It’s been a couple years since I was messing around with buffer weights on a 223/556 AR pistol I no longer have. That must be how the 5.6 ounce got in there. If I remember right, I should have a collection of weights available to make it a standard 3 ounce up to the current 5.6 ounces in several weight increments .

So, what weight buffer do you use that works with un-suppressed subsonic and supersonic ammo?

It has a VG6 Epsilon muzzle break on a 10-1/2" Faxon barrel and a non-adjustable gas block.

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I personally haven’t picked up a 300BO (it’s on my list), but buddies of mine that run SBRs in 300BO run H2 or H1 buffers when unsuppressed, heck I want to say they don’t change their buffers even when suppressed.

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IMG_1084

I don’t personally own an AR-15 other than my M&P 15-22 (blowback operated). So I have no input here at the moment. Gonna watch and see if i can lear somtin :wink::clinking_beer_mugs:

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:joy: Bahahahaha

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I looked to see what I have for materials.

The buffer with no weights is 1 ounce. I have a 2 ounce weight that fills the buffer, 1+2= 3 ounces (standard weight).

I have 3 weights @ 1.5 ounces each. Stacked together, they are the same height as the 2 ounce weight. (1.5×3)+1= 5.5 ounces (H3)

If I cut the 2 ounce weight into 1/3 and 2/3 sections, then I will have roughly 0.7 ounce and 1.3 ounce weights available.

1.3+1.5+1= 3.8 (H1)
0.7+(1.5×2)+1= 4.7 (H2)

Yeah, I think I can get there from here :+1:

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Sounds like that would work! :+1:

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you might want to try a heaver slug in sub sonic rounds

with the issue of ‘‘stove piping ‘‘ and not locking open

points to too lite of load or too heavy of spring

[not enuf back pressure]

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I have read the subsonic rounds have less powder producing less pressure than the supersonics. The 150 grain supersonic rounds have been cycling perfect with the H3 buffer.

Are you suggesting they put more powder in a 220 grain vs. a 200 grain? Or maybe the slower 220 grain provides longer gas pressure dwell time?

One other data point - I am using 300BLK specific magazines.

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Things just got easier, I took apart another 3 ounce buffer and it has 3 equal size weights so I don’t have to cut anything :+1:

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it takes a little more pressure to push the 220 grain down the barrel

and it will be a little bit slower so longer pressure time to get it to cycle

or purchase another spring and tune it to the sub sonic 200 gr

it will still run the 150 gr but might ‘‘slap’’ the action a little more

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Alright, I got out to the range today with an H2 (4.6 oz) buffer, a Std (3 oz) buffer, and materials and tools to put an H1 (3.8 oz) buffer together.

My test protocol was to shoot one subsonic round (200 grain, 1,000 ft/sec) and see if it had enough recoil to lock the bolt back on an empty magazine. Several shots with the H2 buffer yielded no lock-back. I then changed to the Std buffer with identical results.

I then ran similar tests with 150 grain 1,900 ft/sec ammo. It was happy with the Std buffer and the H2 buffer. I think I’m done with subsonic ammo for a while.

Edit: BTW the low right hits were the subsonic ammo, the “almost” bullseye was the 1st supersonic ammo shot. Now in defense of the subsonic, I zeroed with the supersonic …

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