I do my load tests at the lands. When I have a powder charge I like then I adjust seating depth to tune the load in .005 increments.
Trying to many combination's at once will have you going around in circles (I know...I have tried this).
.617 @ 100 with a factory rifle is damn good. If you are expecting groups in the .2's or .3's from a factory rifle then your hopes are to high. Factory guns that shoot consistently small groups like that are anomalies. I have shot 1 hole 5 shot .25 groups at 100 with factory rifle but could not repeat the feat on a consistent basis.
If I can get 1/2 - 3/4 MOA groups consistently out of my factory 22-250 at 100m I am ecstatic.
it isn't going to be a 100yard gun. that's why I want my groups to shrink so when I go out to 400-500yards I will still be able to hit a 2" target.
If you want to shoot a 2" target at 400-500yds on a
consistent basis then you had best have yourself a match rifle built.
For example, F-Class scoring rings are 1/2min V-bull and 1 min Bull rings. At 400m the V-Bull is 2" and the Bull is 4" (within a few thousandths of an inch), at 500m the V-Bull is 2.5" and the Bull is 5". Most competitors shooting these ranges have a tough time shooting perfect strings (all in the V-Bull) and these are with custom built match rifles on a calm day....throw some wind and mirage into the equation and a 1/4min rifle is now lucky to hold the Bull Ring.
I myself have hit gophers with my factory 22-250 out to 435yds. I know I could not do it everytime I pulled the trigger at that distance considering that if a cow farts in the next field over, it will blow that 50 or 55 grain pill 3"s or so off target.