Re: Rechambering from 25-06 to 243???
Keep in mind that a barrel chambered in 6mm Remington will still be shooting good when the .243 or a .243AI will be laying in the junk pile. The neck and shoulder design is the reason why. The long neck will make seating long bullets much easier. If I were doing an improved 6mm round I think I'd have to give the old 6mm Rockchucker the nod. It's very similar to a 6mm Ackley, but uses a 30 degree shoulder instead of a 40 degree shoulder. You'll have less trouble with the dreaded doughnut. Also set the chamber up for a .266" neck diameter, and shave the necks to .264". You'll never regret the move.
I've been saying it for years that Savage needs to do the 6mm Remington. It will work well in the short action due to the slight added length of the reciever. Still if your going to use the rifle for deer as well as varmits, I'd seriously have to consider the .257 Ackley