What would cause this?

[Longcarbine]

Took my new to me .300BO AR pistol out for sight in today and it ran flawlessly, no failure to fire, feed or eject but every case mouth had this flat spot on it when ejected. Any ideas as to what could be the cause.

[bangbangping]

Any ideas as to what could be the cause.

Yes. Firing a 300 Blackout round in a 300 Blackout AR is the cause.

(we should start a drinking game)

Edit: It's extremely common, due to the shorter 300 BLK case rotating into the deflector. Look at your deflector and you'll see brass marks. Some folks put on a piece of Velcro to cushion it.

[dellet]

Any ideas as to what could be the cause.

Yes. Firing a 300 Blackout round in a 300 Blackout AR is the cause.

(we should start a drinking game)

[20X11]

Short answer... this is NORMAL.
Long answer...since the 300blk case is shorter than the 5.56 case the shell deflector was designed for, the edge of the 300blk case hits the deflector and gets dented. No harm done.

[dellet]

Short answer... this is NORMAL.
Long answer...since the 300blk case is shorter than the 5.56 case the shell deflector was designed for, the edge of the 300blk case hits the deflector and gets dented. No harm done.

[20X11]

I'm a bourbon guy anyway..

[TRshootem]

That's an easy fix if you want to stop the mouth dings on your brass....Bicycle tube patches, cut to fit the flat surface profile of the case deflector/dingerizer. Yep, cut it to fit nicely on that protruding thingie, clean up the attachment area, then peel and stick. LOL, I have one on my BLK pistol and a LW 5.56 carbine upper, neither of which deform my carefully, almost religiously pampered cases

PS: My patches were blue, but a black permanent marker made 'em blend right in. I have had only one shooter notice my 'fix'.

[TRshootem]

Dellet: The winds were so strong today(45 mph gusts), the brass never touched the ground. Seemed to me that they were trying to catch up to the mother bullet. Of course one needed to stand in the gale, facing ejection port down wind a bit. Seriously stupid day to prevent your ball cap from landing in Chicago.

[John A.]

^I don't own safe queens