The easiest way to fireform is to just use 243 brass. We use H380 and a 100gr bullet seated to the lands. Forms cases perfectly and is extremely accurate as well. We always have a 100 fireform loads ready to go when we go shoot prairie dogs or chucks. It makes the forming process go a little faster and more fun
Out of the 6 243AI's we have here are the avg. velocities:
22" Factory Barrel: 70 gr BT's @ 3850fps
26" Krieger: 105gr Bergers @ 3230fps
26" Lilja: 105gr Bergers @ 3247fps
27" Lilja: 105gr Bergers @ 3275 fps
28" Lilja: 105gr Bergers @ 3317 fps
28" Kreiger: 105gr Bergers @ 3310fps
All of the 105gr loads are using the same charge of RE-22. All but the factory barrel are 1-8 twist.
It all depends on what you want to use the rifle for. With the factory barrel (1-10 twist), you can probably stabilize up to a 95gr Berger depending on what elevation you are. We have shot the 87gr V-Max at just over 3800fps with the 28" barrel rifles. The Lilja is a 3 groove, and it pretty much destroys the bullets. Half of them don't make it to the target and the other half aren't real accurate. The Kreiger shoots them just fine. I have a Broughton that should be here next week to test against these barrels. I will post info on that when I get her finished up. We my other broughton barrels, they seem to be 70-100 fps more than the Lilja's we normally run. Accuracy is even with both barrels. Since it will be a coyote/tactical rig, I wanted to see if I could get the same velocity with a little shorter barrel.
This is a very accurate little cartridge that is not finicky at all. Brass life is good. We had one barrel with almost 1700 rounds through it and was still shooting tiny groups at 100. We replaced it with a faster twist.
Oh, and it does a number on deer and antelope with the Berger. I have shot antelope out to 580 yds and they instantly are on the ground.
Hopefully I have answered some of your questions.