Dave, if I understand you correctly, the answer is you should have good contact between the breech (attached to the barrel) and the standing breech portion (the part attached to the stock). You will have to use transfer media (smoke, sharpie, etc.) and a mallet, and tap and carefully remove metal to get a good fit. I would aim for good, i.e., at least 95% contact. You may have to upset the 'hook' portion of the breech a bit when you're done to make the thing lock up correctly. Just take your time, and remove a little bit of metal at a time. Good luck!