I to am shooting a 264 Win Mag. My go to load is W-W Case CCI 250 primer & Nosler 120gr BT with IMR 4350 60.0 gr Max load in Nosler reloading manual. I have used this load on Antelope to 500 yds & complete pass through. I am planning on using it on Mule deer this fall. When at 100 yds it averages under 1 inch. smallest group to date .55 inch. Still working on seating depth & have some Nosler Brass coming in mail from Natches Shooting Supply. I hope it helps with group size since all my Brass prep is just sizing & trim to length. I to have thought about using Hornadys 123 gr A-Max for the B.C. but unsure if it would be relaible on Big Game. My Rifle is Model 70 XTR 24 inch Barrel.