new here, some friends told me to come here & ask this question:
what causes 2, 180 degree apart "twist" marks on the head of a fired round ??
i am in the market of buying ARs, particularly interested in pre-bans, one i test fired a few days ago showed those marks, at the very end of the deepest part of the mark there is a tiny cloth snagging burr....
i have removed the bolt, it is clean & burr free, in fact it was very smooth, extractor was clean, sharp squared edges & no burrs, ejector also smooth & tight fiting, the case nor primer shows signs of high pressure.., is this a head space problem ?? or is it just a real big "nothyng to worry about" thyngie......??
thanx, i lyke the forums, they seem so much more interesting now that i am after a 20 year lay off begining to exercise my 2nd amdt. rights......
see ya in the ammo section next
Are you talking about the case or the bullet?
I assume you’re talking about the headstamp area of the case head.
I get similar marks. These seem to be caused by sharp edges on the boltface where the extractor and ejector are located. You’ll note that the extractor and ejector are more or less 180 degrees apart.
These edges dig into the brass case head a bit as the bolt turns to unlock, resulting in two twisted gouges. (I suspect there might be a bit of residual pressure pushing the case head into the boltface as the bolt turns.)
What you describe doesn’t sound abnormal.