My grandson was shooting some RORC 5.56mm L2A2 NATO ammo in his Bushmaster AR 15 yesterday when he experienced a blown primer. Did not discover the blown primer until we were policing the brass after he had finished firing.

On checking other cases fired, most had a shiny spot wiped on the head of the cases, likely from the ejector.

I haven't had much AR experience, but the older gas guns (M1 & M14) were pretty hard on brass,too,but I can't remember ejectors marking the case head. As I recall, the extractor did a number on the case rim.

Is the ejector mark on AR brass normal or is it a pressure sign? Anyone else have any problems with the surplus RORC ammo?

Regards,
hm

I wouldn't shoot any more of the ammo if it were my rifle- you have classic signs of too much pressure.

Thanks, Duane, I agree, the blown primer is absolutely a pressure sign (or insufficient headspace); in either case rest of ammo will definately not be fired.

Guess my question is more about the scuff marks on head of the other cases. In any other rifle, these would be an indication of pressure. Does the AR usually mark case heads on normal pressure rounds?

Regards,
hm

I don't see any unusual case head markings in either AR15s or the registered 16 I own unless the brass is very, very soft. Some surplus ammo seems to have softer brass ... I try not to shoot that. Everything gets tested through an AR first!

Could it be you are firing 5.56x45 ammo in a rifle with a commercial .223 chamber? They are not the same particulalrly in throat depth. Mil spec 5.56 is loaded to a bit more pressure than commercial .223 Remington. .223 in a 5.56 chamber is ok, the inverse could cause the problem you describe.

An AR usually doesn't leave any different bolt face markings. It could also be as suggested the throat on your rifle is short, causing the bullet to be jammed into the rifling and therefore raising the pressure. Also if this happened after firing a magazine and the round sat in the chamber for a little extra time the chamber heat and the powder used could be the culprit. Shoot one round from a cold barrel if there are ejector marks return the ammo.

If it's a Bushie upper, it's 5.56 NATO unless it's a match or CMP upper. If that's the case, it's chambered for .223 Remington.

Maybe soft brass. Had it happen with WCC 99 back when everyone was worried about Y2K and stocking up. Quality control was a sometimes thing.

quote:

Originally posted by MichiganScott:
If it's a Bushie upper, it's 5.56 NATO unless it's a match or CMP upper. If that's the case, it's chambered for .223 Remington.

I think Planemech, Duane and Scott may have hit the nail on the head. This is a match grade rifle, not the standard Bushmaster and the RORC ammo would, I am sure be the 5.56mm Nato.

Thanks, guys.

Regards,
hm