Looks the same as the chamber that was on my Kimber 257. I sent it back they told me tough [bleep] it's within specs. I hope it turns out better for you.
Kimber Classic .308 with marked tight spot 2" from muzzle. Shot 1 1/2" on a good day. Kimber with same response, it's within spec. Theirs, maybe. Not mine.
23" Broughton 5C fixed that problem. Sub half inch.
DF