Marks on 1x Fired Brass

HuntND

Sergeant of the Hide
Full Member
Minuteman
Jan 27, 2018
152
16
40
North Dakota
Could someone tell me what these circular marks are on my 1x fired brass? There not on all cases but noticed it on a few. Possible case stretching to much? They grew .003-.004” fire forming in my chamber.
 

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