FTF with new Centurion upper

[maximus83]

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?

[markm]

You need to be more specific on what FTF you're getting. Next round sticking in mag? sticking at Feed Ramp? Not stripping out of the mag at all?

Does the gun lock back if a single round is loading and fired in a mag?

Nothing in your combination of part should be causing this.

[w3453l]

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).

[maximus83]

Mark, updated the OP--FTF=failing to strip next round from mag. Didn't try the test you suggested, but will next time out.

[maximus83]

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.

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.

[everready73]

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.

Easy first step would be to try a known good BCG and see if anything changes

[maximus83]

Easy first step would be to try a known good BCG and see if anything changes

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.

[Disciple]

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?

[Dutch110]

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.

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?

[maximus83]

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.