I was doin some measuring with my stoney point guage on my 243 win Savage model 10 and to the rifling I was getting a reading of 2.7, so if I back off 20 thous that would get me a reading of 2.68, the book says OAL of 2.64. I am using a Hornady 75gr HP, do the lighter bullets need a bit of a jump before hitting the rifling. DOes anyone load theirs closer or further and find that it makes more accurate?

Best thing is to experiment with seating depth once you have worked up a good load and find what works best in your rifle. Each rifle is a rule unto itself and what works in one may or may not work in another. Only way to know for sure is to try it out on paper.

I don't think there is really a rule of thumb, all rifles are diff. My 260ai is throated for the long 142grSMK. I've shot some of the 85gr Sierras that are waaaay off the lands & they shoot into the 0.3s.