All things AR-15 and variants from newbie to advanced. Find answers here.

[Bang]

Bill Wilson developed and offers the .300 HAMR. Designed to easily convert an AR15 to .30 caliber, it uses a barrel change and the original 5.56 bcg. He offers cartridges, components (such as bullets designed for it by Lehigh Defense), dies, gauges, and complete rifles. AR15 mags work but allow only half capacity. .300 Blackout mags work fine.

https://youtu.be/u69ZzdZni28

[azmule]

Recently finished my first (semi) self-built AR. "Semi" because I used a pre-built PSA upper, 20" 5.56 barrel with rifle length gas system, nitrided BCG - and I used a carbine buffer assembly with 3oz buffer. First 100 rounds, in mag loads of 1, 2, 3, and 5 rounds... feeds good, accuracy is good, but recoil seems a bit harsher than my much lighter 16" carbine, doesn't seem to be any clear pattern in where the cases land, and every case has a dented shoulder, looks like they're maybe hitting the deflector bump. Also, randomly with several different mags, bolt will fail to lock back on empty maybe 10% of the time. I.e. *feels* like harsh recoil for 20", but *acts* like undergas/short stroke. Plan A is to try a heavier buffer, maybe it's not so much short stroke as *hard* stroke? Any other ideas?

[arjohnson]

Recently finished my first (semi) self-built AR. "Semi" because I used a pre-built PSA upper, 20" 5.56 barrel with rifle length gas system, nitrided BCG - and I used a carbine buffer assembly with 3oz buffer. First 100 rounds, in mag loads of 1, 2, 3, and 5 rounds... feeds good, accuracy is good, but recoil seems a bit harsher than my much lighter 16" carbine, doesn't seem to be any clear pattern in where the cases land, and every case has a dented shoulder, looks like they're maybe hitting the deflector bump. Also, randomly with several different mags, bolt will fail to lock back on empty maybe 10% of the time. I.e. *feels* like harsh recoil for 20", but *acts* like undergas/short stroke. Plan A is to try a heavier buffer, maybe it's not so much short stroke as *hard* stroke? Any other ideas?

Harsh recoil usually means over gassed, but the bolt failing to lock back usually means undergassed. 20* AR*s are soft shooting and should function fine with any standard 5.56 round, at least everyone I*ve ever owned and shot did.

Maybe try using it with a rifle buffer tube, buffer, buffer spring and stock. The 3 oz carbine buffer and spring may be your issue.

[cdi]

What stock are you using, collapsible or fixed?
What length action spring, carbine or rifle?

A standard carbine buffer weighs 3.0 ounces.
A standard rifle buffer weighs 5.2 ounces.

A rifle action spring is a couple inches longer than a carbine action spring and both the springs and buffers are not interchangeable between rifle and carbine.

[markshere2]

Stainless split ring in the handguards that will accept them. Slings snap, tie, or thread onto the ring.

[azmule]

Collapsed, which I'd prefer to keep. Standard carbine tube, spring, and buffer, which everything I've read says should be fine with 20". Hate to think I have to go to a fixed stock just because the barrel is 4" longer. Plan A is still to buy-n-try an H1 or H2 buffer by itself, and see what changes.

[Emptymag]

Just a couple links where others have asked the same question.

https://www.ar15.com/forums/ar-15/20...be_/12-699465/

https://www.rimfirecentral.com/threa...rrels.1281336/


https://blog.primaryarms.com/guide/h...buffer-weight/

[Jhaydeno]

Collapsed, which I'd prefer to keep. Standard carbine tube, spring, and buffer, which everything I've read says should be fine with 20". Hate to think I have to go to a fixed stock just because the barrel is 4" longer. Plan A is still to buy-n-try an H1 or H2 buffer by itself, and see what changes.

You don't need to change, I've got a few 18 & 20's with midlength and rifle gas tubes, all include collapsable stocks and run of the mill carbine buffers. The giveaway is the poor ejection of the brass and fail to lock back. Check your chamber size and that the BCG runs smoothly through the upper. I've seen tight chambers that 'grab' ammo, and I've seen bolts, especially plated ones, like chrome and NIB, that physically won't fit through an upper. Cycle your BCG with the charging handle, 'feel' and look for scrapes and interference, and check your used brass for scrape marks (drop a few back in too). Finally, remove the buffer spring and make sure the buffer moves down the tube without interference. I saw a buffer tube that had machine ridges down the entire thing. It worked, but it sounded worse than a washboard in a country band as the buffer slide back and forth.

[arjohnson]

Collapsed, which I'd prefer to keep. Standard carbine tube, spring, and buffer, which everything I've read says should be fine with 20". Hate to think I have to go to a fixed stock just because the barrel is 4" longer. Plan A is still to buy-n-try an H1 or H2 buffer by itself, and see what changes.

As you said try a heavier buffer. PSA AR*s are known to be over gassed, my 10.5* was way over gassed, had to take front sight tower off and put an adjustable gas block on to get it to where it*s supposed to be.

[azmule]

Follow-up report: I ordered the next step up H buffer, and finally got out to the range to try it today. Recoil is tamed down to what I would expect of an AR, it does still eject into the 4 to 5 o'clock zone, but instead of every case hard deflector-dented, there is a much lighter mark in maybe 1 of every 10. 80 rounds fired in loads of 5 (to test the hold-open) resulted in zero failure to feed or lock open. Rifle groups an easy MOA using a bipod too, so I'm happy!