[MikeG]

To Bill and everyone,

How does the diameter of your expander compare to the bullet diameter?  If it's not a good 0.005" less than the bullet diameter, I'd consider trimming it down or replacing it with the Lyman "M" equivalent.  With compressed loads I'd want all the neck tension I could get.

Even if you just barely bell the case mouth, the rest of the neck could be large enough that it's not getting a good grip on the bullet.

Just a thought...

 

[MikeG]

Doesn't sound like the expander is the problem.  .427"-.428" should be just about perfect with .432" bullets.  You must be compressing the powder quite a bit.  I don't have much experience in this area so can't offer anything else than to suggest backing off the powder charge a bit.

I the opposite approach to Jim on the seating punch.  Instead of drilling out the middle, I grind off the outer lip so it's completely flat.  Sounds like either will work, at least with SWC's.  For the LFN/WFN, I would think that a completely flat seating stem would be the better way to go - just personal opinion.