Welcome aboard. Hmmmm, trying to shave <0.25" off of <1.0" @ 100 with a 338 RUM sporter! That's getting down to the fine points!
Assumptions:
Stock pillar & skim bedded
Stock is a proper one for the 100yd bench shooting.
Also, if u're shooting from a bipod, i like Froggy's advice about preloading it in the article on 6mmbr.com-- "bugholes From Bipods." (Kyped from sscoyote's post on another thread)
Proper barrel break in
Barrel is free floated except for maybe an inch or so ahead of the receiver.
Action and bolt are mated/trued/squared(Blue printed)
Primers seated w/a hand tool
Scope at least 14X with parallax adjusted out.
Fine cross hair reticle or very small dot
There is never any wind when you shoot
Shooting from pedestal w/ears up front and sand bag in rear.
Shooting from very solid bench with a decent seat
Chrono says SD and ES in single digits (not absolutely necessary @ 100 yds.
Probably a 12" twist for the short bullet? But the twist is more than likely 1 in 10"?
Brass is properly prep'd to the goal you have.
Loaded rounds are straight.
What if you looked at things just a bit differently? How about a goal of 0.75 MOA instead of 0.75" @ 100. Move your target out to 300 yds and you may already be there. The 338 RUM isn't much of a 100yd cartridge and with the 210 weight bullet it's a bit handicapped down range. 300 yds is a good distance to analyze performance with the cartridge.
Lastly the bullet you chose may well not be the one that gets the last little bit of consistency in your rifle.
HTH, I've just been there and done that w/a 338 RUM project. I never did get the bullet I wanted to shoot even 1 MOA at any distance but got the one I should have chosen first shooting pretty well for what I use its intended use.
