FTF with new Centurion upper

[Dutch110]

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.

Can you put one of the other BCGs in that rifle and manually cycle and see if you get the same symptoms?

[maximus83]

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?

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.

[Dutch110]

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.

[Disciple]

Resistance is only at the very start when retracting the CH, feels normal after that.

Check the cam pin and cam track?

Is there anything unusual about the shape of the carrier or hammer that could cause the two to bind up a bit?

[maximus83]

Can you put one of the other BCGs in that rifle and manually cycle and see if you get the same symptoms?

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.

[MegademiC]

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?

Im wandering if the extra force and light buffer are outrunning his mags.

I had this happen before, a reliable 16" with car buffer cut down to 11.5 and a silencer added cause weak ejection and ftf.

Slow motion iphone footage showed the bolt coming forward before the shell ejected fully causing weak ejection and would outrun the mags randomly.

An h2 solved the issue.

[Disciple]

Im wandering if the extra force and light buffer are outrunning his mags.

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.

My results:

Current 3gun rifle, BCM Lower, JP silent capture buffer assy, Geissele SD3G trigger, BattleArms 45 degree CASS semi auto safety, BCM Mod 3 CH, BCM upper, Lancer 15" carbon fiber FF tube, JP LMOS carrier, BCM bolt, cam pin & FP, melonited BCM 18" SS410 rifle gas bbl with VLTOR low pro GB, Surefire 212 muzzle brake. Lubed with FIREClean. Ammo = Hornady Steel Match 75gr HPBT and PMC Bronze 55gr FMJ.
4200 rounds = no malfunctions

Old 3gun rifle:
Lancer lower, VLTOR A5 buffer and receiver extension, Geissele SD3G trigger, Battle Arms 45 degree semi auto safety, JP LMOS carrier, BCM mod 3 CH, BCM bolt, cam pin & FP, BCM upper with Lancer 15" carbon fiber FF tube, BCM SS410 16" midlength w/SJC Titan muzzle brake. Lubed with WeaponShield. Ammo BH Blue Box 55gr FMJ, PMC Bronze 55gr FMJ, PMC XTAC 55gr FMJ, Hornady Steel Match 75gr BTHP, BH MK262 Mod1, Federal XM193 55gr FMJ.
15,876 rounds = 1 stoppage due to case separation (Black Hills blue box 55gr FMJ which split exactly in half and was a LC once fired case which likely went through a M249)

My accuracy was dropping off on the 16" gun and went up to roughly 2-3MOA depending on how hot I got the bbl. I had the bbl reprofiled to .630" between the gas block and chamber. I believe this contributed to the accuracy variance with heat. So on my new 18" I left the bbl unmodified.

I've run LMOS carriers for 7yrs now and have used them before with adjustable gas blocks and don't recommend the adjustable gas blocks for LMOS carrier on 3gun rifles. Too finicky, example they might run well while standing, but when prone or roll over prone can/will cause stoppages. To me the benefit of the slightly lighter recoil isn't worth the more finicky reliability.

[maximus83]

^They told me the gas port is .075, they intentionally go with smaller sizing so it should not be over-gassed.

[markm]

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.

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.

[w3453l]

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.