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My nice CMP barreled receiver has not been running right from the very start. I have finally figured out the chamber is the problem. I think I need a finishing reamer or perhaps a nice buff job on the chamber. Ejected brass has scars on the shoulder and I think the chamber may well be pitted? scared? etc? Any suggestions, please. I have the tools to jerk the barrel off, so is that next? Thanks guys.
You can try some 0000 steelwool on a long cleaning rod with out handle. Use a used short 30 cal bore brush. Remove barreled action and strip action. Run brush down bore and exit chamber. Put a small amount of 0000 oiled steelwool on the used bore brush spin the rod with brush with a hand drill at slow speed making sure you protect the muzzle from spinning rod. Work the wool back and forth in the chamber. Stop and check every few seconds to see if the chamber looks clean and happy. Do not put to much wool on the bore brush as it will bind in the chamber and twist off the shank of the bore brush. If you have a flex shaft you can do this from the receiver end. A chamber reamer is a last resort as it will only correct raised metal problems but one mistake and you will have screwed up the headspace. Good luck and hope things work out for you.
Edit: After a bit more thinking on your problem are you sure the damage on the brass is from the chamber or is it from charging handle strike on ejection. Look for the brass dots in the charging handle area of the op rod. If you find them then that may be how the brass is getting dinked, can you post a photo. You can make some proving ( dummy ) rounds. Size fired cases ( 8 ) leave new primers out and seat bullets without powder. Polish one shell till it is like a mirror. Load them in an en-block polished round on top. Load rifle with these dummy rounds and slap the bolt to chamber a round. Now slowly retract op rod to eject round over a towel and inspect the round for all marks. This will tell you if the marks you are finding are pre or post ejection.
I believe that all the .308 insert bbl.s were stamped with the modification, but always something to look for if it has issues in the shoulder area.
Best to try cleaning up with the bbl. on, first. Taking it off and then putting it back on might cause more issues. It might not time the same.
If the chamber has issues, you probably had a false reading on the headspace. You will have to clean the chamber well, then check headspace again.
HTH
Mark