Well, it happened. First outing with with new SBR.

Specs:
QC10 Glock Lower
H2 buffer
carbine spring in carbine length tube
7 quarters in buffer tube

What should I do, in addition to ordering a new catch/detent/boltcatchspring?
Heavier buffer, more quarters, ?

Thing that stinks is I know it must have happened on one of the last mags of 250 rounds, so now I have to put it through its paces again to prove reliability...

I got a Glock lower with out an active BHO..
I would try a heaver buffer to fix your problem.
As well as more quarters, to limit the rearward free movement.

I've had luck with the Seekins brand bolt catch in my colt pattern lower. It's supposedly made out of tool steel. Has worked for me along with a 9mm Q-buffer.

Yeah I emailed QC10 support, and they have been very responsive, and are sending me a replacement bolt catch spring. And apparently they have updated it since I bought my lower, so hopefully lrbho will be running more reliably.

Also, I found that I should be running a heavier buffer (my H2 is like 4.5 oz) closer to 8-10 oz. Went ahead and ordered a KAK 8 oz 9mm buffer, that is longer than 5.56 buffers to avoid smacking the bolt catch (don't need quarters now). That buffer is cheaper than most H3s I could find anyway.

Ordered a wolf extended power spring on my same order as my plunger and catch (went Seekins as well).

Hopefully all that takes care of it.

Sounds like that should do it. I broke two bolt catches before I changed over to the Seekins and Q buffer. Those standard bolt catches I used would only last two or three hold opens before snapping.

Great.

What brand lower are you running?

Double Diamond. QC10 took them over I believe? Don't quote me on that though...

You are correct.
I think they have an updated LRBHO arm/mechanism that you could upgrade to if you have any sort of irregularities with it.

Common issue in 9mm and 308 builds.  Get a bolt catch made of tool steel.  I know V seven weapons systems makes one.

seekins is supposedly stronger than most.

http://www.seekinsprecision.com/enhanced-bolt-catch.html

A heavier buffer should resolve your problems. Search over in the http://www.ar15.com/forums/f_3/15_Rimfire_and_Pistol_Calibers.html forum because other folks have encountered this problem.

Already got an 8 oz 9mm buffer at my door (kak industries + USPS priority, Cali to Houston in 2 days). Just waiting on my replacement bolt catch and spring from QC10.
BTW, UPS is worse than USPS IMO.
Thanks though.

I know this is a little late but....I used to stack quarters behind the buffer spring, I would continuously break bolt catches,  went thru four as a matter of fact in probably two months.  Keep in mind this was an h3 buffer, wolf xp, and 2.75$ in quarters, it put me about a 1/4" or so back from the bolt catch.  I did have an 8 oz buffer but at the time did not use it becuz I had other issues and the stacked quarters seemed to function the best. ...except I kept bending, snapping bolt catches.  

I think the quarters put alot of preload on the spring, and as far as I saw it, that was what was bending my bolt catches as that force came to rest on lrbho.  Long story short I fixed my chamber issues, started using 8oz buffer with the Seekins and life is great.  I personally don't see the Seekins breaking, that mutha is beefy.  Just my xp.