Need to go with a heavy bullet for caliber with some powders...especially the WC872 surplus and similar grades. 264-6.5's may do much better with 140 grainers.
AA8700 is an option for the .264 mag. The stuff is very slow burning like H870. Magpro looks like it'll work well in the .264 mag case as it seems to work well in the .270WBY case (very similar cases). The book says that 65.4 grains of Magpro will drive a 140 grain Amax to a little over 3,000 fps with a 24" barrel. I think that's a little slow as my .270 mag will push a 150 grain bullet faster than that. 8700 seems to be best suited for the very heavy bullets in a long barrel.
gary
In my pre-64 Winchester Model 70, with factory 26", found after trying varous powders that IMR 4350 is the best in it. I use winchester cases and CCI 250 primers behind a 120 grain Barnes Tipped TSX Boattail, 3480 FPS and .6" three shot groups at 200 yards.
