J. Jones,
My gunsmith has had a 50 bmg improved reamer for about 10 years! He says that it will push a 750 Amax at 3350 from a 32 inch barrel. I have held the round in my hand and it is AWESOME! It eliminates all the case taper and looks like it is ready to kick some serious butt! He has reamers, dies, and all the know-how to put one together for you! His name is Brad Stair and he runs a shop called, "performance guns". He's from Texas, then moved to Colorado, and now he's in Utah.
He also has reamers for the 408 Chey Tac improved!