For MOST caliber changes in the AR platform, you will need a new bolt (not bolt carrier), magazines, barrel, and maybe a heavier buffer to lighten recoil.
Some calibers like the 300 AAC blackout, 7.62x40 Wilson Tactical and perhaps a couple others use 5.56 brass and claim to use 5.56 mags. So with these calibers you would only need a barrel (possibly the buffer too).
TO THOSE WHO ENJOY THAT FOR WHICH THEY HAVE NEVER BLED, DON'T THANK THOSE WHO HAVE, THEY BLED NOT FOR YOU, BUT FOR EACH OTHER.
Last edited by TacticalGenius; 07-08-2012 at 16:57.