Robert

I'm sorry. I forget this thing replies to the last person that posted. None was directed at you. Just general thoughts.

FWIW in your case are you sure you are touching rifling or are you touching the throat? I had a very similar issue in where I thought I had the chamber designed a certain way. It was. Found out the bullets I was using were .0003 larger than others I was using and I was reading off the sides of the throat. Its why I never got a pretty rifling mark either. I just shot that rilfing the way it was supposed to be.

If I were you, I'd find out what the exact chamber dimensions were and at what length you should be able to seat the lapua bullets.

If in the end the throat needs to be longer it can be cut.

Jeff