FTF with new Centurion upper

[maximus83]

As someone who has been running the A5 system exclusively for well over a decade I can tell you that for some odd reason guns get more reliable with the heavier buffer weights on the A5, even small gas port barrels. I did some testing with some small gas port midlengths: a 0.072" 16" mid and a 0.075" 14.5 and found that my ejection pattern got more erratic and weaker as I went down in buffer weight and when I went to the heavier H3 or H4 the ejection pattern and recoil impulse seemed more consistent and finally settled on running H2 or H3 as my preferred weight for almost all guns.

I know its counter intuitive because if you think you are undergassed you should be going with less buffer weight not more but with the A5 I have found that running something like the H2 weight tends to fix problems that only appear with the lighter buffers. I don't know what the principals are behind it(maybe some engi like Lysander can explain) maybe some momentum based or lock time thing but I have found the H0 buffer weight actually cause MORE problems in ALL guns regardless of gas port sizes.

Try it with an H2 and your Centurion bolt carrier, you might be surprised with what you find. I pushed my small gas port barrels all the way up to H4 weight with zero issues with the caveat only some increased muzzle dip but the guns actually felt that they ran smoother. Just when you think you understand the AR you can still run into voodoo magic things that dont make any sense.

Sounds good, that was my original thought to try. The heavier BCM buffers mentioned in the OP came in today, AFTER I got home from shooting. So will try those with the Centurion BCG next time out.

[Clint]

You've got the issue isolated to the BCG, which is good.

Centurion should take care of it.

Got to take it out for a 2nd try today, tried a few things. I think it's short-stroking, because of the BCG.

1. Fire one round only from mag. Result: never would lock back with the ammo types I tried earlier, or any .223. So with that and the original behavior, seems certain it is short stroking.
2. Swapped out the BCG for a known good LMT BCG. Result: issue solved. I couldn't get it to fail with any type of ammo.

...

I'll talk to them Monday and see if I can get a return on the BCG. But curious now if this will turn out to be a "by design" issue, and I'll keep the upper but simply have to run it with a different BCG.

[calvin118]

I had the same issue years ago with a centurion arms 14.5 inch barrel. I worked up the issue similar to you. It turned out that the brand new BCM bolt carrier group that I was using was at fault. I sent the BCG in to BCM and they replaced it quickly. I never received an explanation but the upper has worked quite well ever since with the replacement BCG. I presume there was some kind of leak or defect in the gas system of the BCG.

[maximus83]

Centurion is taking the BCG back and will give a refund. I'll probably get another BCM or LMT to replace.

[markm]

Centurion is taking the BCG back and will give a refund. I'll probably get another BCM or LMT to replace.

I'd love to know what the deal was with the BCG.

[Dutch110]

I'd love to know what the deal was with the BCG.

Ditto. Given I have several of them running this exact same setup with no issues. Would love to know the cause. Given the level of goodness that is Centurion I would not hesitate to ask them to replace it for me.

[markm]

Ditto. Given I have several of them running this exact same setup with no issues. Would love to know the cause. Given the level of goodness that is Centurion I would not hesitate to ask them to replace it for me.

Agreed. I'd have just done a swap-a-roo!

[Dutch110]

Agreed. I'd have just done a swap-a-roo!

My guess is someone got heavy handed with the Permatex and clogged the gas key hole. Should have told him to fish some trimmer string down the gas key to see if it was obstructed. Can't believe I forgot that one loll

[Disciple]

As someone who has been running the A5 system exclusively for well over a decade I can tell you that for some odd reason guns get more reliable with the heavier buffer weights on the A5, even small gas port barrels. I did some testing with some small gas port midlengths: a 0.072" 16" mid and a 0.075" 14.5 and found that my ejection pattern got more erratic and weaker as I went down in buffer weight and when I went to the heavier H3 or H4 the ejection pattern and recoil impulse seemed more consistent and finally settled on running H2 or H3 as my preferred weight for almost all guns.

Were you using a LMT Enhanced Carrier in any of these? I recall that BufordTJustice liked to combine the A5 system with these, and found that heavy buffers required no more gas to operate than light buffers.

[Dutch110]

Were you using a LMT Enhanced Carrier in any of these? I recall that BufordTJustice liked to combine the A5 system with these, and found that heavy buffers required no more gas to operate than light buffers.

I think the longer spring combined with what feels like a more progressive nature means that it take less force to begin moving the buffer in its rearward path. Not apples to apples but in my x39 builds I started with the A5H2 and at the advice of the guy who cut my barrel, moved it up to an A5H4. It wasn't bad at all with the A5H2 and functioned fine. But the difference in felt recoil going to the A5H4 was noticeable. That's a pretty big jump in weight with no difference in function. Which kind of supports the theory you mention.