I think there are 2 things going on here. First of all, if you check the diameter of the Berger bullets, I bet you find the are .0005" smaller. So the Hornady are probably. 243 and the Berger are probably. 2425. Secondly, I will almost guarantee you have carbon build-up in the throat. It may not actually be a ring yet, but I bet if you soak the throat area with carbon remover and brush it well, use stiff nylon not bronze brush, you will see a lot of carbon come out and your bullets will fit better in the chamber.