FTF with new Centurion upper

[DoubleW]

I’m currently shooting a factory Centurion 11.5 (.069 gas port) on an SBR lower with carbine RE, H2 buffer. I only use Gen 2/3 P mags. 480 trouble free rounds of Hornady M193. I will say it’s probably the softest recoiling 11.5 I’ve ever shot, but it’s been reliable and slings brass out at 3 O’clock. Next time I go out to my range I’ll throw it on an SBR Mk2 BCM lower and see what happens.

[Disciple]

I would suggest trying it out on a lower with carbine extension.

It should be sufficient, and a lot easier, to use the appropriate spacer in the A5 tube and a carbine spring and buffer.

[1168]

When you say its failing to strip the next round from the mag, are you saying that the bolt is appropriately behind the cartridge, but not shoving it forcefully enough? Or is the bolt bypassing the cartridge on the way forward, partially or completely?

[Dutch110]

This is perplexing. There is nothing different in the design of the Centurion upper that would differentiate it from every other design out there that I am aware of. Gas port size is gas port size. .070 range is not too small or too big. Given the uppers in question are factory Centurion uppers the gas blocks are most likely tabbed and pinned so it's probably not a gas block alignment issue. Centurion BCGs are just good, milspec phosphate and chrome lined BCGs. I've swapped out carbine length systems for A5 systems on several rifles now with no adverse effects. One, last flier here. Can you look at the back of your bolt lugs and see how they are wearing? Only other thing I can think of is the barrel extension is out of spec causing the hitch in the unlocking you are feeling when manually cycling. Causing it to slow down just enough to short stroke. Also, have you checked head space?

[ODgreenpizza]

Check for gas leaks between the tube/block and block/barrel.
Check gas tube is alignment.
Does the fired brass look normal, maybe it's sticking?
Check the inside of the RE for high spots/roughness and proper depth.

[maximus83]

When you say its failing to strip the next round from the mag, are you saying that the bolt is appropriately behind the cartridge, but not shoving it forcefully enough? Or is the bolt bypassing the cartridge on the way forward, partially or completely?

BCG rides over top of mag and goes into battery without stripping a round. But does this sporadically: maybe 1/2 to 1/3 of the time. Besides trying different mags, I also tried a 10rd mag, and a 30 only loaded with 20.

[w3453l]

It should be sufficient, and a lot easier, to use the appropriate spacer in the A5 tube and a carbine spring and buffer.

I didn't know such a thing existed, but yeah by all means if it's easier then worth a try.

[w3453l]

This is perplexing. There is nothing different in the design of the Centurion upper that would differentiate it from every other design out there that I am aware of. Gas port size is gas port size. .070 range is not too small or too big. Given the uppers in question are factory Centurion uppers the gas blocks are most likely tabbed and pinned so it's probably not a gas block alignment issue. Centurion BCGs are just good, milspec phosphate and chrome lined BCGs. I've swapped out carbine length systems for A5 systems on several rifles now with no adverse effects. One, last flier here. Can you look at the back of your bolt lugs and see how they are wearing? Only other thing I can think of is the barrel extension is out of spec causing the hitch in the unlocking you are feeling when manually cycling. Causing it to slow down just enough to short stroke. Also, have you checked head space?

If I'm not mistaken, the A5 extension reduces bolt speed correct? I know there's a more elaborate explanation, but that's pretty much it in a nutshell right?

It is perplexing for sure. The 11.5 Centurion that I mentioned above went over 1500 rounds without cleaning; I *think* I put a few drops of lube on the BCG through the ejection port at some point, but that was once and not a proper full relubing. After swapping the extension I took it out to the desert with two cases of Wolf Gold + some random onesies and twosies of different boxes of brass cased ammo. This was high desert; very windy, very dusty. The rifle sat out in the open on a table when not used. It didn't have a single issue.

When I got it home, it was obviously dirty from all the carbon buildup and dust. While going 1500 rounds between cleaning isn't a crazy feat. I think if the gas tube, gas block, or barrel extension was on the ragged edge of spec (or out of spec), it would probably start having failures when dirty.

This is of course speculation, but I'm wondering what about the A5 made such a night and day difference?

[Clint]

Was the BCM BCG just manually cycling or a test firing?

Is the friction present with an empty chamber?

Markm is right; this combo should run, so if it doesn't run there must be something wrong.

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.

[Dutch110]

If I'm not mistaken, the A5 extension reduces bolt speed correct? I know there's a more elaborate explanation, but that's pretty much it in a nutshell right?

It is perplexing for sure. The 11.5 Centurion that I mentioned above went over 1500 rounds without cleaning; I *think* I put a few drops of lube on the BCG through the ejection port at some point, but that was once and not a proper full relubing. After swapping the extension I took it out to the desert with two cases of Wolf Gold + some random onesies and twosies of different boxes of brass cased ammo. This was high desert; very windy, very dusty. The rifle sat out in the open on a table when not used. It didn't have a single issue.

When I got it home, it was obviously dirty from all the carbon buildup and dust. While going 1500 rounds between cleaning isn't a crazy feat. I think if the gas tube, gas block, or barrel extension was on the ragged edge of spec (or out of spec), it would probably start having failures when dirty.

This is of course speculation, but I'm wondering what about the A5 made such a night and day difference?

It doesn't necessarily reduce bolt speed. It's a more progressive spring over a longer length which means it absorbs energy better than a carbine set up and reduces felt recoil. It's less snappy if that makes sense.