Failure to go into battery

[Growler]

LR55,
Did this happen with a low mass carrier? Non-mil primers?
Thanks

[LR1955]

LR55,
Did this happen with a low mass carrier? Non-mil primers?
Thanks

Growler.

Nope -- standard mil spec bolt carrier, Grendel bolt, Lapua brass, CCI 450 primers.

No one was able to figure out why it happened so it remains a mystery.

LR55

[BluntForceTrauma]

Last time I bought a firing pin I think it was about $6, and I might even have a spare lying around. Seems some guys create a dummy firing pin by grinding down the tip until it no longer exceeds the boltface for cycle testing live ammo in the house without fear of accidental discharge. Useful, or a waste of time?

[NugginFutz]

I’d say useful, BFT.

I’ve given it a bit more thought, and realized that without the firing pin in place, the hammer can travel further forward than normal. I can’t say with certainty what might happen with a fully assembled AR, but I have seen firsthand what happens one accidentally presses the trigger with the lower separated. Without the BCG and firing pin in position, the hammer impacted the bolt catch, breaking it off. I don’t know if it was the combination of the two being absent that allowed the hammer to travel too far, or just the firing pin, but I personally wouldn’t want to risk it.

With respect to a modified firing pin, I’d also suggest either blueing it or otherwise marking it in such a way as to make it easily identifiable. I don’t think there is any need to detail the various reasons as to why such a measure is desirable.

[Kswhitetails]

The solution to this is a $2.50 firing pin filed .070 short. Paint the thing red to identify it, and keep it handy when this kind of testing is required. Just a quick thought about how to overcome the rotating cam pin issue.

[ecosystem3]

As a followup, I had the rifle out this weekend and it ran like a champ. I removed the extractor o-ring and there were no more jammed BCGs going into battery. I put 60 rounds through the barrel and was eventually shooting MOA.

While debugging, I did try to slide the BCG into battery without the firing pin and a few times the cam pin did rotate and lock the bolt. After some praying and jiggling, I was able to remove the BCG. A spare firing pin has been ordered.

Again, thank you all for your input and guidance!

[Kswhitetails]

Hot dang! Glad you found a solution that was painless! Great news. Forward, ho!

[Mad Charlie]

E3:
I had the exact same problem on my first Grendel build, and solved it in much the same way. Tuned and polished the extractor, and de-burred the extractor slot and ejector channel in the bolt, and removed the "rubber baby buggy bumper plug" from under the extractor. I replaced the spring with an "extra power" spring from Brownell's. The rifle has run flawlessly ever since, and very smoothly I might add. Little things add up with these rifles, but once they are tuned right they will run fine.