AR Trouble Shooting

Probly nothing wrong with your build. Ammo is the suspect. What brand is it? I have bunches of wolf and herters in 7.62x39 and .223 that gave us same fits. Put some extra power hammer springs in our mini's and the problem went away.

Both mini's would fire brass ammo all day long.

Edit, didnt catch the part about the other gun. Maybe you do need a stiffer spring/heavier hammer. Are you getting primer strikes? Have you tried rechambering it after you wait for possible hang fire?

I'm betting it's a combination of hard primers in the ammo and an underpowered hammer spring in the rifle.

Make sure the hammer spring is installed correct.

I am also running my bolt dry.

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Right there's your problem.

Lube the BCG like every manual, NCO, and experienced shooter tells you to.

If you have a .223 case gage, drop the steel ammo that did not fire into it. It may be a slightly undersized, giving you excessive headspace and a longer distance for the firing pin to reach the primer.

I have a Lake City round that did not fire with only a tiny firing pin mark on the primer, and when I checked it with the case gage, it turned out be way too short!

I had the same trouble with monarch brand steel case and a 4 lb spring.

Just to clarify, the round appears to be chambered and when you pull the trigger, the hammer falls but no boom? Correct?

First thing to check - is the cartridge actually in battery. If the bolt is not completely locked (the cartridge is a tiny bit too long for example) the AR15 firing pin will not protrude (to limit out of battery detonation)

Second thing to check - is the primer indented and if so, is it the light little mark left by a free floating firing pin or a good, solid strike on the primer?

If your weapon is firing brass ammo with no problems and only this anmo causes an issue, it is 99.9% likely the problem is the ammo and troubleshooting the rifle won't help much.

Chrome bolt & carrier dry. Usually an issue. Usually you won't get as many rounds through as you did. doesn't happen as much after several hundred rounds, but they don't like dry too much. My 2 cents... and I've been there.

rhp997 said:

Update to the problem- switched out the lower and functioned properly. I believe the problem is a weak trigger spring. Ordered a new one from Colt.

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Hammer spring.