buy or rent
there is a company that rents reamers for most cals, 60.00 for 10 days, brownells sells a kit for 180.00. I just installed a 12 51 barrel in my mixer im muilding, HS perfect and clocked up after 1 torque and retorque, noted in wrapper te was1...long headspace from factory. Install and ck HS...you may luck out. If you do ream buy the brownells set and resell on cmp m1 site....someone listed a 1 time used last week it lasted 7 min before it was sold....130.00 USAF2