49/50 grns 2209 usually works (take care, that's getting to the limit). Have you adjusted the lead to see if that makes a difference? The Berger site gives some advice on this. They can be finicky. You might want to try Nosler BT. They just about always shoot well.
R15 was accurate in my last one but I couldn't get the speed. 2208 is probably the most common powder used in 7/08.
The other thing is that you need to be sipping a Late between test shots, and cock your right little finger slightly while you are firing the rifle.
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