Start with cleaning the chamber by hand with a chamber brush and CLP, then get the chamber dry before checking out the conditions of the chamber.

The chamber should be mirror smooth, with no reamer chatter.

If the chamber has deep reamer grooving/chatter, then you may have to send the barrel back for a replacement barrel.

If the condition of the chamber is just light marking, the chamber is not chrome plated, then it may be possible to polish the chamber instead.


The best way I know how to polish is a chamber, it a 22 cal nylon brush with 0000 steel wool wrapped around it to build up a plug on the nylon brush the size of the chamber, then with it on a section of cleaning rod, use it for spinning plunging strokes in and out of the chamber a few times to final polish the chamber.   Here, you are only doing a final polishing of the chamber, and will not over size the side wall dimensions of the chamber dimensions instead.

Lastly, even with the chamber polished, you still need to run the upper receiver bearing areas wetter with CLP as well.

To add, in some cases if the extractor spring is weak with the extractor slipping of the rim case at extraction, you can increase the tension on the spring by adding a #60 O ring (costs about a dime at any hardware store) around the extractor spring.