I Know!! I Know!! Ask Me!! Ask Me
Yep. I've done a bunch. Mine and my customers. It makes quite a difference when you take the time to notice.
A 451 or 452 bullet comes out of a 449 throat at .... yep you guessed it ... 449. Then it goes into the barrel and just sort of skids and slides. The bullet may "up-set" in the bore and actually pick up a spin but will wobble on the way to the target. A 451 or 452 bullet will also be a little reluctant to pass thru a 449 throat. Bumps chamber pressure. SO:
Rreameing the throat will reduce immediate chamber pressure and allow the bullet to properly enter the forcing cone. This will initially reduce felt recoil. Since the bullet is not skipping and sliding through the bore, it reduces leading. Since the bullet is properly sized to the bore, accuracy is improved.
I have found ALL of these things to be true and opening the throats to be very beneficial. At 6 paces from the targets, after the buzzer goes off, you may not notice any of this. For CAS you only need minute of pie plate accuracy. However, it will lessen the stresses on the gun. Get your reamer from "Manson Reamers." DO NOT EVER turn the reamer BACKWARDS.