Which batch did you find the huge variance with??? Woodleighs or Core Lokt???
I don't normally shoot out past 300 yards, give or take 25 yards as I'm not much good at predicting trajectories beyond that consistently. Some people can and do it regularly.
I've never had an issue with the Remington Core Lokt bullets out to 350 yards for accuracy, other than my own inability to judge bullet drop successfully.
I'm thinking, because of the load of 2208 that you're using 140 grain bullets??
With that bullet and that load, if you're shooting from a 22-24 inch bbl you should have appx 8 inches of drop at 400yds and maybe a bit of drift due to the spin of your bullet but MOA shouldn't drasticly increase.
I use a very similar load for my grandson's and stepdaughter's 7-08 Rem chambered Mod 7 rifles that I built for them. The last couple of hundred rounds I loaded for them was 41.0 grains of Varget over CCI250 primers.
Both of these rifles have Shilen Match barrels and their chambers have been cut with the same reamer and care was taken to keep headspace within .001 of minimum spec. The reamer dimensions are tight as well for the rest of the body, shoulder and neck dimensions. Both rifles accept the same handloads and shoot them into sub moa groups right out past 350 yards if the shooters do their part.
Maybe you're having consistent ignition problems from your primers?????
There's really no reason those bullets, which are notoriously accurate, should be losing enough velocity for the groups deteriorate, from where they were at 100yds.