I know a feller that fireforms 9.3x57 brass out of 8x57. 14 grains of bullseye and a small wad of toilet paper. Puts it in the gun, points it in the air, and pow.
Ain't no sense to be wasting real bullets.
Or, if it's just a little off, you could try this.
I ran a 30 caliber plug down some 7x57 brass, and then backed the die all the way out, and sized the neck down a little at a time, checking after each reduction. Eventually I had a case that the neck was skinny enough that the cartridge would go far enough forward for the bolt to close. The shoulder was not back where it belonged, though. I had, in essence, made a false shoulder for the rifle to headspace on.
Load it as normal and fire.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.