5.56 case rim?

[deolexrex]

Ok first the run down...

S&W M&P Sport
either WWB 5.56 or Federal XM193
other than Magpul furniture and a Colt carry handle it's bone stock

I'm just up over a 1,000 round, no feed issues to date and it pretty much hits where I point it (when I do my job)

Last night I ran a couple mags before dinner and when I was policing the brass I noticed something on the case rim.



Note the cut in the 12 o'clock position. Is this normal?

[Spot]

Hmmm. . . looking forward to hearing the answers.

I hope that's not considered normal, because I intend to reload all my 5.56 brass.

[jet80tv]

I don't know what causing that but I've never seen it on my brass. Have you inspected your brass previously and not noticed this? If it wasn't there before then that should tell you it's not "normal" however the abnormalcy being a bad thing is another question. Do those marks exist on the unfired cartridges?

[bull8042]

I can only offer more speculation, but the second cartridge in the pic appears to me to have been damaged by an impact due to the "mounding" of material on both sides of the inclusion. The only thing I can think of off-hand would be the case striking the edge of the ejection port after firing. That would require a rather odd ejection, and something I have never seen myself though. Might be worthwhile to inspect your upper around the port to see if there are any "brass tracks" that you wouldn't expect to find.

[deolexrex]

Ok, you made me think of something else. My son has the exact same carbine and his cases eject at about 1 to 2 o'clock (if the muzzle is noon) and mine eject at about 3 or 4 o'clock.

I'll check my rifle for "brass tracks" I have it with me at the office today.

[deolexrex]

I just looked... I don't see any brass shaving or filing in or around the bolt, BCG or ejection port, maybe a little on the deflector but I don't see any "edge" there capable of cutting the brass.

Weird...

[bull8042]

I just looked... I don't see any brass shaving or filing in or around the bolt, BCG or ejection port, maybe a little on the deflector but I don't see any "edge" there capable of cutting the brass.

Weird...

Hmmm, that is weird. The only other thing that came to mind was maybe a burr on a magazine feed lip. It just doesn't look like that kind of damage could result from anything in the magazine, one due to the location, and two the extent of the damage. There just isn't enough force there to displace that much material.
Sorry, I definitely don't know what else to tell you. Perhaps someone with much more experience than myself will chime in and help you out.

[deolexrex]

I only have P-Mags. It seems unlikely that they could ding a case.

[x-STG1]

I'm betting it is caused by the edge of a bolt lug when stripping the round from the mag. As to why, maybe the round is binding in the feed lips and the extra 'umph' needed to strip it is causing the ding?

[deolexrex]

I just looked at the bolt face under a bright light and I can see some "brass" on the bolt face.

What does that mean?