Magnum primers are generally used with hard to ignite powders or when powder volume is large. Since a 223 powder volume is not large, I would use a ball powder. W748, H335, BL C2 and AA 2520 all use a CCI 450 primer in the latest Speer Manual.
Starting loads in Speer Manual #14 for 50 grain bullets:
W748 - 26.5 grains
AA 2520 - 26.0 Grains
BL-C2 - 25.5 Grains
H335 - 25.0 Grains
Good Luck and Good Shooting