I am running 92gr H1000. I am getting about 1" Groups at 300 yards. Velocity is around 2750 out of a 26" tube as I recall.
Firearms stand next in importance to the Constitution itself. They are the American people's liberty teeth and keystone under independence. The very atmosphere of firearms everywhere restrains evil interference. - George Washington
Peace is that brief glorious moment in history when everybody stands around reloading.' -Unknown
That says it all about H1000 in your gun. I can only hope mine does that well when I get it.
My barrel is a Lilja 1-10 twist, *8 contour w/28 1/2 barrel + Muzzle Brake. I'm pretty sure H1000 is the way to go, but would like to hear about folks using the Retumbo. If all else fails...I will try both powders when I get the rifle.
Not 338, but I have tried both in my 7mm STW. I can get higher velocities with the Retumbo than the H1000. If I continue to load up the H1000 attempting to get close to launching a 168 gr Sierra MK at 3200 fps as I get with the Retumbo, I start getting severely flattened primers and I get nervous about pushing any harder. The best velocity I can get with the H1000 is about 3080 fps.
I assume the same relationship between the powders would exist in the 338.