New Magpul UBR-2 bolt not locking back on PMAGS

[Iraqgunz]

Something isn't right. My reasonable deduction meter says that when it was working before and not working after the mod, then I have to think there's something to it.

[gunnerblue]

My UBR2 locks back on Gen 2 30-Rd PMAGS, Gen 3 20-Rd PMAGS, USGI aluminum and a Lancer AW5

[jerrysimons]

Try a carbine length buffer and spring using the spacer.

[M4Fundi]

Try a carbine length buffer and spring using the spacer.

That would be a bad idea

[jstalford]

That would be a bad idea

Why? The UBR2 comes with parts to run either a5 of carbine.

[jerrysimons]

That would be a bad idea

Don't you suspect the length of the buffer tube to be an issue? Try it with the spacer and shorter buffer.

No way your gun is undergassed or oversprung running a Novekse barrel with blow hole for gas port and only a A5H2 buffer.

[RobertTheTexan]

The BCG locks back perfectly manually on both GI & Pmags... i swapped BCG , CH, complete upper, lowers and manually all is GTG.

Only when firing with Pmags does it not lock back.

VLTOR has me taking measurements next week and

Magpul says that it MUST be a gas issue and that either the bolt gas rings or poor ammo is to blame

Ill check next week when i get back

I experienced the same issue on my UBR 2 setup. 12" LaRue barrel, A5H2 buffer standard A5 spring, LMT FA BCG. I noticed it on Gen2 and Gen 3 windowed PMAGS. I didn't try my Lancer or USGI. I thought it might be a new ammo but after thinking more on it I am positive I shot this ammo prior to the UBR 2.0 without any issues. Left me scratching my head, but I didn't have time to start swapping out parts. That same training day I was running that ammo in my 11.5 SBR but with a DD barrel, A5 tube, enhanced LMT FA Bolt Carrier w/standard LMT bolt.
I tend to agree with IG. Nothing in my 12" SBR is old enough to be worn out, the UBR 2 is the only change introduced to my setup.
I did an eyeball compare of the UBR tube and the A5 (Vltor) I pulled off and they appeared to be right st the same length. Could have been a small variance I suppose.
Not sure I agree with Magpul's assessment because my BCG has a pretty low round count and it all worked as advertised two weeks ago when it wore a SL-S stock on an A5 tube.


Sent from my iPhone using Tapatalk

[jerrysimons]

Well this is disconcerting. Was about to pull the trigger on a UBR2, will wait till this gets sorted out.

[jstalford]

I will mess with mine hopefully this week on a 12.5 suppressed. But it's a new build so I won't have anything to compare it to before.


Sent from my iPhone using Tapatalk

[fledge]

I'll test mine out today. I haven't used a pmag with it. The lancer has been flawless.

ETA: After testing, 30rd gen 2 and 10-20-30 round gen 3 pmags work well with mine with manual cycling. I'm running the A5 system.