That souns like the number. Lots of blokes are using it in 416 Rigby..around the 50 grains

But if you have something like a 416 where you could jam the bullet into the rifling then 50 grains of 4227 or 2204 would probably be OK. No go with 378 or 460 as the rifling starts .75" from the case neck.

The problem with the flake shotgun/pistol powders is you are restricted to about 1300 f/s

I have used 60 grains of 4227 in a 460 with 400 grain Speer and filled the case with cotton wool and that worked but it looked like a snow storm.

Mike