txpitdog, the 300 Win. conversion may work just fine, but the .264 and 7 mag cases are identical in size and offer (me) more peace of mind on the feed rail issue. For certain, if you find a .264 that shoots, and the barrel is still good, the conversion is just to scratch an itch.
I guess that I was unlucky with my .257 Mk V back in the eighties as it did not shoot good groups with factory or hand loads - at least the ones I tried. I did have good results with a 7 and .300 Wbys., and both had a lot of freebore. jack