Because H4350 is hard to find here, I developed loads with R19 in my 260A!. It works well, gives good velocity and is fairly temp stable. I don't leave the ammo in a hot truck or anything but it seems to shoot very well with 130 Bergers and 143 ELDXs.
I would add N160 and N165 to this list. Regards JCSH4350 is the go to powder for the .260 (have several) however, there are others that perform just as well. H100V, IMR 4350, H4831 SC, RL19 H414 and others. The .260 is a very good round. I have shot it with all of the listed powders with 10, 1123 and 140 class bullets to 1000 without issue. With the 140's and 139's I would look at the H4831SC, not overly fast, but produces accurate rounds.
I hear youLike everybody else. H4350 is a clear favorite for performance. Have your wife get a second job and pay a premium for it if necessary.
I hear you
Since I'm shooting in the .150 range when I'm not being a retard at 100 yards and around 3 at 500 I'm Happy as I know what the weak link is - it ain't the powderI can hopefully fix that.
I'm learning Randy, slowly. I shot in my very first groundhog match the 1st. I have learned that it is rare to have good conditions here and mirage still gives me fits.500 yds would be more like .750 and up with a .015 100 yd group but way less than 3 with the same conditions and good bench form.