Take a loaded round and lay a bullet next to it with the tip of the bullets even. If the boat tail is at or forward of the shoulder neck junction then the dounut should not affect the round. If your seating deep then it can become an issue.
Mauser06 is correct. You do not need to pin the lug as long as you use the new style wrench from Southland. They have modified the wrench to hold the lug in the correct position. The original wrench did not do this.
Try measuring the brass along the body of the case. I have heard of issues when brass is fired in another rifle that the bottom of the body being a clearance issue. Once fired it will form to the new chamber.