My Noveske 300 Blk won't lock back on last round , *FIXED*

[Paintguy21]

Rifle: I built this with genuine Noveske parts.

Noveske 16" stainless barrel pistol length gas system. Surefire MB762-211C Brake
Noveske marked MUR upper/13.5 NSR
Noveske Gen 2 chainsaw lower,milspec extension ,carbine spring, H2 buffer.
LMT enhanced full auto BCG.

Ammo:
My loads 175 smk
18.5 gr A1680
Functions fine, won't lock back on last round.
Great accuracy

Factory Barnes 110 blk tip
Functions fine, won't lock back on last round.
Great accuracy

Things I've tried:
Carbine buffer ( no change)
H buffer ( no change )
BCM full auto BCG/ carbine, H, H2 buffers ( no change)
Old bushmaster commercial BCG / H buffer ( stove piped/ crushed cases) lots of feed/ejecting issues.
Several different mags 20's and 30's USGI, and magpul Pmags.

Checked for proper lubrication, slip 2000 wet BCG.
I used the gas block that came with barrel, and the included pin, so it is aligned properly .

Should I try an H3 buffer?
I will be using a Surfire Mini 762 when I get my Form 4 back.


I'm not ruling out it may need to be broken in ( less than 75 rounds so far)
The only thing that is troubling , my buddy built one with the same barrel ,upper , lower, and his locks back using factory rem 115 supers. He only shot 5 or 10 through his.

I am stumped.

Any help would be much appreciated.

[-k-]

Does the bolt catch move freely? A small flaw in the casting can cause it to drag and not engage.

Is there anything attached to the bolt catch?

[Paintguy21]

Its a phase 5 bolt catch . Also have a Raptor charging handle .

I'll take a look at the bolt catch . I could swap lowers with my buddy, he has a regular bolt catch .

If that's not it , I'll swap charging handles .

It has to be something minor, other than not locking back , it runs great .

Thanks for your reply

[Paintguy21]

It was the Phase 5 bolt catch.
Oddly enough this lower would lock back with my 556 upper, but not the 300 Blk.

Put the regular bolt catch on , it was good to go even with subs.
Also put a magpul bad lever on still good to go. Go figure.

Thanks to my buddy Casey, for swapping out all his parts until we found it.

Thanks K you were spot on.

Sucks because I loved that phase 5, but I like a working rifle better.

[-k-]

There is some interesting stuff happening with those bolt catch levers. Sometimes they work great, sometimes not. If I made them I'd consider spending some time with a bunch of different guns and a high speed camera to try and shed some light on what is going on.