Hi looks to me the chamber was cut with 2 different reamers or drilled part of the way then finished reamed the defining line is too sharp and square to be done by swarf jammed in the reamer flute. Part drilling the chamber with the wrong drill and trying to finish with a chamber reamer will give you the same effect you have on your brass, to fix your problem is more than 1 turn setback I would cut the whole threaded section off re-chamber and refit properly. I have been fixing stuff ups by so called gunsmith's for over over 40 years and this is fairly common, you only noticed the problem because you wish to reload, if you did not pick up and inspect your cases, you would not have known you had a problem, any responsible gunsmith would have test fired and inspected all aspects of the rifle and fired cases and rectified any issues before releasing the firearm. Remember firing a rifle is a controlled explosion generating 50,000 PSI +, only inches from your face. JOEY55