Thanks for all the suggestions. What I plan to do is replace a 1-10 twist barrel with a 1-9 twist so I can shoot 62 gr. bullets. I plan to cut the barrel down to 16+ inches and install a factory flash supressor and a factory sight bayonet lug combo. I have all the parts, a lathe, and some guts. I figure that if I measure the case clearance with the old barrel, mark the receiver for the barrel flat, carefully disasemble and reassemble I will be able to tell if I am in the ball park. I have to design some sort of barrel vise and receiver wrench.