If you are looking for maximum velocity 4350 is a little on the fast side to accomplish that, for max velocity I'd start with h4831 and then start looking at some slower powders powders, I started reloading at a young age about 71 or 72 under my dads supervision, over the years I started collecting reloading Manuels, I have most them old and new, going back to the 50's, odd thing about the 264 is how the data has changed, looking at one of the most recent manuels compared to the same manufacturer of the 60's and 70's I find that there is 9.5 gr difference in the max loading, in favor of the older books, this might be explained in lot to lot variables, new manufacturer vs military surplus, however in the same two books I find this same powder in another caliber to be a half grain heavier in favor of the newer book, last fall A hunting buddy inherited a 264 M70, we found that the charges from those older manuels were not only safe but the velocity was higher than listed, of course these older books don't include the newer powders of today but we found powers like re22 and 25 H1000 vit n560 165 &170 to name a few really elevated the velocity to a new level, unfortunately it was at this time we became aware of the components drying up so we put that project on hold, before we did we were finding most loads producing well over 3400 fps with 120 and 125 gr tsx and partition bullets, all were tested for safety by firing 5 sample cases for a total of 6 times primer pockets remained tight, I would be interested to find what others may have found when using this cartridge.I'm definitely interested! Getting ready to work loads for my dad's pre-64 .264 WinMag. Have a box of 121g Hammer Hunters and thinking about starting with H4350.
I like what I see. Been running 160 matrix over hodgdon powder and have gotten great results. I would like to see your results its hard to find compotes to load anymore.