Hi 480:
I like W748. With 40gr. V-Max I use 30.0 in my M77 MkII VT. 3,550 at muzzle and, believe it or not, have 3-shot groups at 200 meters of .450". I DO NOT use magnum primers, but if you start down a couple of grains and work up, they should be OK.
With 50gr. V-Max I use 28.5 of W748. 3,375 at muzzle and also very accurate: .250" at 100 yards is common.
I use LC military brass mostly, flash hole deburred, neck turned enough to get out any high spots and sized in Lee Collet dies. CCI 400 primers. One of the beauties of 748 (and BL-C(2)) is how well they meter through a powder measure.
Good luck, and enjoy the .223! The M77 is an excellent rifle.