Finally, picked up my 300 rum.

First thing after cleaning is finding the OAL. Saamie says 3.6, but my remington hits the rifling at 3.8 inches. I won't be able shoot for a while since I am having eye surgery, but I am working up loads, so when I finally am able to go to the range, I can test several.
I am backing the bullet off the rifling by 0.020 inches. Since it is a magnum, should I try 0.025??