I have a 26 inch barrel on my Remington 700 .22-250 Varmint with a 1:14 twist.
I've tried several powders but so far my Remington seems to like Reloader 15 better than any of them, but that might be the result of the long barrel.
I am about to try Vhita Vuori N140 in the .22-250 because I have had incredible results with my .308 in recent testing.
For 40 grain bullets, I've gotten the best good accuracy loading up into the 3800 fps area when I chronographed them. Best loads average between .3 to .4 at 100 yards as long as the wind isn't too strong.
Nosler Ballistic Tip bullets seem to work the best and they act like a grenade when they hit a varmint.