I would take a look at R17 as well. I think many people expect more velocity from it so put the pedal to the metal.
But there is enough tested data to verify at least an additional 50 fps or so in the cartridges that it's a good match for.
Check out the loads for the .260 R it is at 2,912 fps. on the Alliant site. The loads shown for the 6.5 are for military actions. The 6.5 should easily equal or slightly surpass the .260 at the same pressure due to 5% more capacity.
From what I gather R17 is close to IMR 4350 in temperature sensitivity but not as consistent as the H version. Most of the high power shooters seem to be using H4350 for 120-139 gr. bullets in the .260. Usually about 42-43.5 grains.
"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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