450Bushmaster.net

I was getting ready to drill/tap a fireformed case today for use with the Hornady O.A.L gauge and on a whim tried to put a 300 grain XTP Mag bullet in the case mouth but it wouldn't fit. Is this because of the straight walk of the cartridge and it's chamber? How can I expand the case mouth without resizing?

My experience has been that unsized, fire formed cases usually pass a bullet into them. You could try chucking a dowel of the appropriate diameter the when wrapped with some wet-or-dry sandpaper would fit tightly into a fire formed case and then spinning it in a drill to clean off any rresidue inside the mouth as well as take a little wall thickness off. That could give you enough additional clearance to coax a bullet down into the case with little to no resistance. That's how I made my OAL Gauge case for my 450b testing. Truth be told, the performance of this caliber seems to be far less dependent upon bullet jump than many of the precision bottleneck calibers I reload for. Case in point, I have loaded 300gr XTP Mag bullets actually touching the lands and it didn't do anything for group performance. that particular bullet is the only one I've found that can be loaded into the lands without exceeding my AR magazine limitation. The 300 XTP Mag bullet actually hits the lands in my particular barrel with a COL or 2.22"

If you can't get a bullet to slip into a sanded, unsized case, keep sanding more off the inside of the case or look around for a rod of the particular diameter needed to stretch the case slightly, as long as it will still chamber.

Hoot

Being cheap, have never used that Hornady gage, instead I use a partial sized fired case, seat a bullet long and chamber it into the lands. I mark the OAL with a Sharpie and put it in the die box.