case neck scratches

[caleb90]

just finished my ar build in 6.5 grendel. this is my first build and first ar15. i ran a box of hornady black eld through it just to test. after getting it sighted in i was getting groups the size of a nickle from 100 yards. but i noticed my case shoulders were getting scratched deeply and i had brass on the bolt face? being new to ar's what causes this?

[caleb90]

also i went to post a picture but couldnt figure out how. what am i missing

[Cornbread]

Check the feed lips of the magazine. If they are sharp they can scratch the cases. Also check the feed ramps see if they have sharp or rough edges. As for brass in the bolt face a small amount can be normal. You can check the extractor for rough edges.

[snarkscarbine]

Brass on the bolt face is usually a pressure thing, or just a rough bolt face, but i wouldn't worry about it unless you're seeing other significant pressure signs. Scratches on the shoulder could be a sharp bolt lug in the barrel extension, or a sharp magazine. one way to test would be to sharpie up the shoulder of a fired case, drop the case into the chamber and close the bolt behind it, then cycle the bolt to extract the case at a medium-slow speed, maybe even slow enough to watch the case be extracted and ejected. The idea being to mitigate impacts from other sources like the shell deflector, etc. If you've got a bright scratch in the sharpied area on your case, it's probably from a locking lug.

[Djgrendel]

Was the brass on the bolt face flakes, or rubbed onto the bolt face. Flakes would suggest your extractor is shaving the rim during the loading process. Polish your extractor. Not the lip but the top and bottom corners. Lrrpf52 has the best procedure to cure your feed ramps. Was a while ago. But he referred to it as a melt down. Once you see it, you will understand.

[AR15gunner]

just finished my ar build in 6.5 grendel. this is my first build and first ar15. i ran a box of hornady black eld through it just to test. after getting it sighted in i was getting groups the size of a nickle from 100 yards. but i noticed my case shoulders were getting scratched deeply and i had brass on the bolt face? being new to ar's what causes this?

Do they look like these? [ATTACH=CONFIG]13657[/ATTACH] If so mine had a bad chamber and it was replaced by the manufacturer.