Yes rim thickness will do that,also, some grime under the extractor will cause the same problem. I had a friend have the same problem,and after looking the bolt face over,it had alot of "flakes",or slivers of brass under the extractor. After a good cleaning,and a little oil,it was operating good as new. Alot of guy's clean everything on the gun,BUT the bolt face,extractor,and bolt lug, raceways! Gunk builds up in these areas,and causes alot of accuracy/problems. Ron