I fully float most of my rifles, not because of POI changes when the barrel heats up, in fact a couple of my rifles shoot better groups with upward pressure at the forend tip, but because of changes of POI when the wood takes up or loses moisture eg if rifle stored in Sydney and then taken to the outback where the humidity is low.

I suspect that the two issues are barrel vibration and barrel transit time. Upward pressure could reduce barrel vibration variations between the loads and one would predict that barrel transit time is shorter with a faster powder.

I might try a relatively fast power with the heavier projectile and the slowest possible powder with the lighter projectile as this will increase recoil due to the heavier powder charge.

mike375 may be onto something with his comment about big cases (relative to bore) shooting to the same POI - I've got a 265Win Mag that puts 100gn and 140gn projectiles 2" apart at 110 yards. I might try changing powders etc with it to see if I can get the 140gn up 2-3".

I think I'll stick with ADI powders - I'm tired of working up a load and then finding that the powder has become unavailable.

Thanks to all,

mike