Thanks, Tim. I played around with a lot of ammo, including the Cor Bon that you sold me. Ultimately I ended up using some custom loaded ammo from Hendershots. 400 grain TSX at 2250 fps, 100 fps faster than the Cor Bon. Still need to get set up to reload, though. Not much factory ammo in 404 with premium bullets and what there is, is pricey.
2,250 is my target velocity w/400gr for the 450-400 NE I am picking up soon.
With IMR 4831 or similar it will still be a relatively mild load in the No 1...but just enough extra oomph over the typical double-rifle velocity to convince me I am not wasting ALL of that case capacity!