I got the 338 out today for the first round of testing. So far it's shooting pretty well. This is the only group I shot after moving out to 1025 yards.

I'm not unhappy with that, but I expect it to do better with a little work. I wasn't shooting any of the guns very well today so this wasn't a very fair test.
The real test today was to work up and see what velocities I can get. I started at 130gr of H 50BMG and moved up to 135gr. It looks like my barrel is a little on the slow side since the 135gr charge gave an average velocity of 3038fps with an SD of 8. That's quite a bit lower than I expected. Every Bartlein barrel I've had shot pretty slow and it looks like this one is no exception. Next trip out I'll just step up the charges and see where I end up.