I recently went through this.
I sized the '06 brass in the 7.7 dies (Lee).
I then cut them about 1mm long with a Harbor Freight 2" cut off saw. Trimmed with Lee trimmer.
First shot extracted..... HUH...?! Rifle has been rechambered to 7.7x63; aka 7.7-06, aka .31/06!!!
OH WELL! At least it was only 50. Besides, they had tired necks from being fired in a Garand.