Brand new build…..short stroking?

[camoman]

I just fired the weapon for the first time today. It was about 10 degrees Fahrenheit, a little breezy.
Did a fifty yard zero, and dumped the rest of the mag into the target. Zero failure, seems to group descent.
It didn’t lock back….
The weapon:
Lantac dual charging upper(side and rear).
Break War Hammer charging handle.
16” Ballistic Advantage premium series .223 wylde SS Reece profile barrel, with pinned mid length gas block.
Bear Creek side charging bcg, with BCM bolt, and BCM chrome lined gas key….properly staked using Brownell’s staking tool, and Permatex aviation sealant…torqued to 55 inch pounds.
Aero Precision hand guard.
CoolHands g10 mlock hand guard grips.
JP 3 prong flash hider.
MilSpec buffer spring.
Carbine buffer.
80% lower.
Palmetto polish lpk.
Aero buffer tube.
Magpul stock, and grip.
Holosun AEMS.
Vortex micro 3x.

All parts are brand new, except the stock, and hand guard. Lubed with Lucas heavy duty gun oil.
Zeroed with Winchester 62 grain green tip.
Any theories on why it won’t lock back?
Do I need to play with buffer weights?
Do I need to just put a few more mags through it?
I have never had a new build do this, so I’m in foreign territory.
To be clear, it only took about 8 rounds to zero, only dispatched 30 rounds total, so this malfunction happened only once.

[jackblack73]

What do you mean the BCM BCG was properly staked with a Brownell's tool? Did you stake a BCG that was already staked? I'm wondering if you broke a screw doing that. You're already using a carbine buffer and milspec spring, so I don't see how you could play with buffer weights.

[camoman]

I removed the bear creek gas key, and installed a BCM, because it was staked very shallow, and not chrome lined. I changed the bolt because BCA have been known to have outta spec lower quality parts.
I would have just bought the corresponding Lantec bcg, but I could not find one.
By playing with the weights, I mean swapping the carbine buffer with an h1. I don’t see why I would have too, but I don’t know.
Maybe it just needs broke in.

[17K]

You have lot to unpack but I wouldn’t start just yet.

It was 10 degrees and it’s a brand new build.

How thick is that Lucas oil?

[markm]

No gun should run best with a standard carbine buffer. H1 minimum. I have one really lean gassed 14.5 that runs with an H1 well, but that's an exception. The H2 is the middle of the fairway with carbine systems.

Does the gun eject snappy or mild?

[camoman]

Well, I zeroed two builds back to back. The one in question has a more sharp recoil pulse, then the other….so yeah I would say it’s snappy. The other has a st-t2 buffer and a tubbs speed lock. Where the one in question has just a standard spring and buffer.

[camoman]

The Lucas oil is good oil, and I’ve seen thicker.
I totally get it’s cold, and she is brand new….but I’ve been here done that with a lot of builds, and never had a short stroke. I think I’m gonna order an H-2 buffer and another Tubbs speed lock.

[MegademiC]

What magazine?
Did you try others?
Does it lock back on an empty mag when you cyle by hand?

[camoman]

Windowed p mag, I did not try others. It does lock back when hand cycling.

[jackblack73]

Initially I thought you were short on gas, but now I think you could be outrunning the bolt catch. H2 will probably help, but you could just try the ST-T2 in it first.