When fireforming with bullets you need a certain amount of pressure to form the case properly. Most cartridge brass will deform at around 50,000 psi at the case shoulder.
So to get this with a bullet you still need a decent load and your still burning 90 grains of powder and spending money on the bullets.
For ecinomic and barrel life reasons, I recommend fireforming with corn meal once the barrel is broken in. For my Allen Magnums they have a limited barrel life anyway so why waste it forming cases when you do not have to.
Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.