case mouth expansion necessary?

[Rocky Raab]

Yup, you're gonna have to flare them, at least a little. If you size a case and then hold a bullet to the mouth, you'll see that the bullet base hangs over the case mouth all round!

The expander then bumps the case out a bit, and a small shoulder on the expander plug imparts a small flare. Adjust that until the rounded base of the bullet JUST goes inside the flare. Correctly adjusted, you'll get the maximum amount of case neck tension without shaving off any jacket material or buckling the case.

Then (as mentioned) the taper crimp will smooth out that flare.