Bullet Seating

[dakotah]

In addition to comments already made:

Are the cases trimmed square?
How much of a crimp are you applying?
When the case is being crimped, does the seater still push on the bullet? Sometimes seating the bullet to the right depth and crimping afterwards makes a better crimp. (Though it requires two operations.) That is if the bullet is being crimped and the case mouth is digging in while the bullet is pushed the case will often bulge.