Just got a Centurion CM4 LW 16" midlength upper, first time out had repeated failures to feed. It would fire a round, maybe two or three, then fail to feed. By fail to feed, I mean failing to strip next round out of mag.
Details:
Gas port: 0.075"
BCG: new Centurion one
Mags: Rotated among three newer Gen3 Pmags
Ammo: BH 77 OTM, Prvi Partisan 5.56 M855
Lower: BCM MK2 (A5) with their T0 buffer (3.8oz) and milspec rifle action spring
Mags and ammo should be ok, full power loads and fired just last weekend through two other rifles.
Contacted Centurion, they said their built uppers and rifles are not designed for A5 system, they build theirs around the assumption of all milspec. So I agree with them, it’s likely not an issue with the upper as built, just that I need to tune my setup to work with this upper.
Assuming best place to start is try a couple of different buffer weights. Ordered BCM buffers T1 (4.7oz) and T2 (5.6oz).
Does that sound right? Anything else I should look at?
I had similar issues to yours. I switched out from the A5 to a carbine extension with Sprinco white and H2 buffer. I’ve put about 1500 rounds through the rifle since making the switch from A5 and had 0 failures since. To this day I don’t know what it was exactly, but the only variable I changed was the A5 buffer system and all my problems went away.
ETA: The failures I was getting started with failure to lock back on empty, which progressed to failures to pick up the next round from the magazine (as the rifle got dirtier).
That’s interesting. Centurion seemed to want me to move away from running an A5 lower setup, they said that they’ve heard a lot of issues with FTF when combining their uppers with an A5 lower setup. They couldn’t really give any advice on tuning for an A5 since they design theirs for 100% milspec.
Yeah my shooting buddy and I talked about that last weekend, unfortunately we didn’t have another 5.56 rifle along. Plan to try that too.
One thing about the BCG: it’s weirdly hard to retract the charging handle. There’s a level of friction or resistance there that I don’t see any of my LMT or BCM BCG’s. But it’s brand new, and I lubed it well, on inspection I couldn’t see any obvious issue with it.
With the A5 system you have extra spring force over carbine, 58.5 vs 50.1 stored energy by crosseyedshooter’s calculation. (BCM Carbine vs BCM Rifle in A5.) Combine this with a peculiar level of friction and perhaps you have short-stroke malfunctions?
Are you running the same A5 setup in the other rifles using those BCGs? A heavier spring/weight will provide more resistance when cycling. Also is the resistance in the beginning of the stroke and then get easier? As in is the bolt having a hard time coming out of lock? Or is it a constant resistance throughout the stroke?
Yes–currently all 4 of my lowers are setup with either BCM MK2 (A5), or with VLTOR A5. Resistance is only at the very start when retracting the CH, feels normal after that.
Hard to say at this point. I’ll try some of the easy button things suggested here. And if all else fails, I can always do what @w3453l did and convert a lower back to a standard/milspec RE setup. To be fair, that’s what Centurion is advising and I will if I need to. But if I can get it work reliably on an A5, I’d rather do that.
I have a 14.5 Centurion barrel (MLGS) using an A5 with A5H2 and Sprinco green set up in one of my rifles. It’s currently running an RCA BCG (so not apples to apples) and it runs spot on both with and without a can. Which is in part what is making me think this is BCG related.
Tried that with a BCM BCG. No difference in the level of friction. I mean the BCG seems to operate fine regardless, only mentioned the friction because it seemed unusual. That may be a non-issue.
I don’t have enough experience to say but it did not seem likely, given “Rotated among three newer Gen3 Pmags” unless seriously over-gassed, given what others run successfully. For example A5 and LMOS without adjustable gas.
That could be causing short stroking if it’s slowing the cycle enough. No reasonable buffer system should have anything to do with this malfunction. Especially since you’re using the correct spring. The middy system is pretty forgiving. My guess is there’s some short stroke issue where the bolt isn’t fully cycling back to grab the next round.
Just to add a little more details to my earlier post; I got interrupted so had to keep it short.
I had an 11.5" Centurion built upper with their BCG. It was put on a Centurion lower with FCD internal parts (FCD A5 extension, Sprinco green A5H2).
As said before, it started off cycling fine. Then progressed to failure to lock back on empty, which then progressed to the short stroking and eventually the BCG was getting resistance when I would pull the charging handle to eject a spent casing.
I tried the following setups:
-VLTOR A5 OEM spring with A5H2
-VLTOR A5 OEM spring with A5H1
-VLTOR A5 OEM spring with A5H0
-Sprinco Green with A5H1
-Sprinco Green with A5H0
All of them had the same problems as the original setup I started with. I popped the upper onto an LMT MARS-L with Carbine extension and carbine buffer and everything started working fine without issue. Mags were all PMAG Gen 3 and some Gen 2. Also, the advertised gas port for the barrel was 0.069.
I then swapped out the A5 extension for an FCD carbine extension with Sprinco white spring and Colt H2 buffer. The rifle ran 1500 rounds without a single hiccup.
I have tried a Sprinco blue spring in it as well for a few mags and everything ran fine.
Throughout the whole time ammo used was Wolf Gold 5.56 (white box), Wolf Gold .223 (orange and black box), and a mix of some other brass cased 5.56 and .223 rounds but in smaller quantities.
ETA: I do remember Centurion telling me that their uppers weren’t designed around the A5 system as well. I didn’t pursue trying to diagnose what was going on after switching back to carbine. I’ve been happy with everything I’ve had from them since and just stuck with carbine extensions on everything since then.
I would suggest trying it out on a lower with carbine extension.