I was about to build a 17 Mach IV, and will do so, but maybe chamber for the new rem factory 17 Fireball. The question is what action to use. I have 2 Remington 600 actions and several 700 SA's available and was wondering if anyone had an opinion as to which would be better suited. They all have the proper bolt face size, and I have several Shilen barrel blanks in .224, in 9, 12, and 14 twist rates. So a recommendation on twist rate would be appreciated as well. Thanks in advance.