Originally Posted by älg
it is based on the 416 rigby according to Norma´s catalog.
The 338 Lapua is also based on the 416 Rigby Case as is the Wetherby rounds, (338/378, 378, 416, and 460)
The only way to get more velocity with less powder is to increase chamber pressure, some people are shooting the 338 Lapua with 300 SMKs 2900 to 3000 FPS, to do this one only needs to accept the higher chamber presures. I am shooting the 300 SMKs out of my 338 Laupa at 2791 FPS, I have ran them higher but the brass requires a lot more effort to re-size if I do that
range it,check the wind, dial in correction, aim and only one shot