This depends on your rifle. I could not get anywhere near my lands, so I started by loading to mag length, and then loaded some up in 1/2 grain increments until i found the sweet spot. i never did have to change the oal, and was able to find a great load by just varying the charge.
a friend of mine just yesterday brought over his 300wby win mod 70 that shawn carlock just put a brake on and did a trigger job. we loaded some 210 bergers to mag length and started with 76.5 grains of H-1000. this is the same load that we shoot out of a rem 700 300 wby.
it was incredible. didnt have to change a thing and this gun shoots 1/2 mo. verified with 3 groups at 100 yards, all right at 1/2 moa. this weekend we will give it a try with some distance.
by the way, shawns work is amazing, this gun shoots so much different than it did prior to the trigger and brake work!
good luck.