i am getting 1/2 groups with my 338 at 100 yds using 88 grains of h1000 seated to mag lenght . should i be working my load up at longer distance like 300 or 400 yds rather than 100 yds since the rifle is for longer distances.
You can do that. There are so many variables to reloading that can change your grouping. Have you played with seating depth any? A 2.5" group is sub-MOA at 300 yards. Is this a custom gun or a factory rifle? Are you restricted by magazine space? How far out do you regularly plan on shooting this rifle?
A lot of people lump all of these variables of reloading and end up confusing themselves. Some people just flat out guess on a seating depth and try it with different powder charges and others try different seating depths first before trying different powder charges with that one particular seating depth that seemed to group best.
I am not a supporter of just pulling a seating depth out of your butt or a seating depth that someone found that worked for someone else on the internet.
I try to find a seating depth that seems to work best with the rifle and then play with powder charges. That way, I am not guessing with anything.
A lot of times people will guess at a seating depth and get a powder charge that shoots well for them but aren't getting the accuracy that they could if everything was fine tuned. It basically comes down to how nit picky you want to be.
To me, how nit picky I get is based on how far out I plan on shooting this gun on a regular basis. If it is a 600 and under rifle, then I wont be too picky. .75-1 MOA accuracy is just fine with me at those ranges but it has to be consistently that accurate. Now anything beyond that range and I am a lot more picky on the accuracy, consistency and the reloading part of it.
Try the different powder charges and see how that works for you since you seem to already have a seating depth that you want to use.