Are you starting with brand new brass? Fired brass could have the web area all out of kilter, especially if they were used in a semi-auto. If so, you'll need a small base sizing die to correct it.

I have a .300 Savage in a 24" Contender barrel, and it has very tight tolerances. But I have formed quite a few cases from new .308 (and a few 7-08) brass with zero issues. I simply run them into the die, trim, chamfer, deburr and load.