Forming 243 40' Improved

[Larryjk]

Westerner2, I chamber for this, and it is also called the 243 Ackley Improved. Like they said, use a faster powder, put the bullet right to the rifling and shoot. The cases don't have to be annealed first, but doing so should have been a plus. When your rifle was chambered was it a new chamber or a rechamber from a standaard .243 Win.? If it was a rechamber, the barrel should have been set back a thread because the Ackley Improved (or the Rem Improved 40') is about 0.004 shorter headspace than the standard. This is so you can put a standard .243 Win. in the chamber and fireform. You should have a little pressure before the bolt handle goes all the way down to battery. You won't hurt the gun. This procedure also insures you will end up with a fireformed case that doesn't have any stretching in the web area.
If you don't have this .004 shorter chamber, you will end up stretching the web and setting back the shoulder each time you shoot the case, resulting in early case failure. If you just case-neck size the fireformed cases, you shouldn't have this problem. Standard .243 Win. cases "grow" so that you need to trim about every third shot. You eliminate this considerably with the improved case.