Briman - you're right - I should have also mentioned seating bullets out to jam into the rifling. I have also known folks to use pistol primers for fire forming, and using a reduced power striker springs in their bolts while doing this - just to reduce the tendency for the firing pin to drive the case forward; causing primer setback. In the case of the Ackley Improved's, the usual headspace setup of the gun not being able to close on a "go" guage and still being able to close (with some effort) on a virgin brass case, will drastically reduce this setback potential.