In my .40 limited guns I had to run a .400 bullet in a barrel I had that was TIN coated. These same bullets will tumble in a new gun with a schuman hybrid, I have to run .401 bullets or they will tumble. Some bullet companies will send you some raw lead bullets, that are softer, that you can use to swage your barrel with to determine the size you need. The crimp can also be an issue, but so is bullet to barrel fit.