BCM Bolt Out of Spec - closes on no-go

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  • SkiPatrolDude

    Ultimate Member
    MDS Supporter
    Oct 24, 2017
    Went to the range yesterday after not having shot my AR's for over a year. One build in particular, built around a Criterion 16in HBAR, I've been less than impressed by the accuracy and had some unusual bolt-lug peening on the rear of the lugs. For context, I built this rifle back when I was still new to the platform and very much learning. I ordered the BCM BCG separate from the barrel, and like the true novice that I was, assumed it would headspace correctly and assembled the rifle worry free. Down the road I purchased a set of Clymer go, no/go gauges and religiously checked headspace for my future builds, but for whatever reason I never went back to check this rifle in particular, having headspaced dozens of builds for myself and friends without a single failure.

    After another lackluster range session yesterday, and with literally every other AR I brought out shooting this one, I decided it was time to tear this thing down and figure out what the issue is. The ammo I brought was IMI 77gr OTM and PMC Xtac, and the rifle shot way better with the PMC surprisingly, but still not great. This is counterintuitive since the IMI is loaded to much tighter tolerances, albeit much hotter.

    TLDR; The BCM bolt goes into battery very easily on the no-go gauge. This then prompted me to try the bolt in every other rifle I owned, and low and behold it closed on all of them. I then swapped just the bolt with a spare toolcraft bolt, and it would NOT close on any of my rifles. I then repeated the process of swapping the problem bolt into ALL of my other carriers (7 total) and it closed on ALL of them. It became quickly apparent to me that it was the bolt that was the issue.

    Looks like I'll be contacting BCM on Monday to see how they plan to handle this.

    Anyone else ever experience bolt peening like this? If so, I'd check your headspace ASAP.


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    Gozer the Destroyer
    MDS Supporter
    Feb 16, 2013
    Calvert County
    The bolt looks shot out. It might actually be under gassed. And there’s several reasons for that. I’m definitely not an expert on that, but Chad (Clandestine) is. I would ask him. He’s on here, and runs the School of the American Rifle. In any event, I think that bolt is trashed. It’s very rounded and worn. Here is a very healthy BCM bolt to compare to:
    Last edited:


    Ultimate Member
    Sep 2, 2011
    Fairfax, VA
    ARs frequently close on no-go and the US military doesn’t even use that gauge. What you need is the NATO field gauge


    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    ARs frequently close on no-go and the US military doesn’t even use that gauge. What you need is the NATO field gauge

    But I still would not want a bolt that failed in every AR I owned and I see no reason BCM would not shoot a new bolt and carrier out to you, post haste.

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