I think that it would be a good idea to keep a spare BCG around. I’d like to get a top-quality BCG to put in one of my RRA rifles, and probably use the RRA BCG as a spare. I’ve not had any issues with the my current BCG so far.
I know that the CMT, LMT, Colt, BCM, or FN Contract BCG’s should all be of good quality. My question is are all these parts truly drop in? I heard someone mention headspace issues when replacing the bolt … is this truly a concern? The rifle that this BCG would go in has about 900 or so rounds through it at this point - it’s still pretty new.
It would only really be a problem if your barrel had thousands of rounds through it. What you’re checking is to make sure that your new bolt won’t close on a USGI 5.56mm NATO Field gauge with an older barrel (much higher round count). If it does then it has excessive headspace which can be dangerous and the rifle shouldn’t be used until you replace the barrel. I check headspace about twice annually (on my stuff) or when replacing broken bolts, it takes me less then a minute so why not check?
Get the 5.56mm gauges and all from the same manufacturer (I prefer Clymer).
GO is to check if there’s is enough headspace (not used much) Brownells part #184-100-007 5.56 NATO, GO
NO-GO to check if there’s too much headspace. Many ARs will close on a NO-GO but not on a FIELD. Brownells part #184-100-008 5.56 NATO, NO-GO
FIELD checks for dangerously excessive headspace. Brownells part #184-100-009 5.56 NATO, FIELD
Ideally you want a 5.56mm NATO chambered AR to not close on a 5.56mm NO-GO as well, sometimes this isn’t easily attainable if you don’t have a lot of bolts to try.