25 grains of 4064 with the 64 should be real accurate...
for those looking to try RL 15, consider AR Comp...
its supposed to be the temp insensitive version of RL 15, tho it does have a little faster burn rate... according to J.B. and a couple of other sources...
for the 63 Nosler Varmaggeddon SP, a charge of 25 grains of H 322 is a very accurate load out of my rifles... all being bolt actions...