The 416 B&M is designed for the Winchester M70 WSM control feed action, with 18 and 20 inch barrels. I found that 20 inches is about optimum, and that with some loads one does start to loose some velocity at 18 inches. However, for a lot of the work done with 416 caliber I am willing to sacrifice some velocity for handling and ease of working in the field. Primarily the 416 B&M is at it's very best with 350 gr bullets. In 20 inches of barrel it runs most 350s at 2450 + fps and in 18 inches of barrel 2400 + fps. More than enough to accomplish most missions with a 416 caliber rifle.
I have an Ultimate stocked version in camo, I figure it's just about a perfect Alaskan rifle. It is only 38 inches overall and weighs 6.5 lbs and launches 350s at over 2400 fps and 300 gr bullets well over 2600 fps. The New 325 gr CEB BBW#13 Raptor it is more than enough for anything one might encounter in Alaska, along with having more than enough range.
Another favorite bullet is the 225 Raptor that runs from 2850 fps in 18 inch guns to well over 2900 fps in the 20 inch guns and will handle everything up to the heavies, buffalo/hippo.
The 416 B&M is quite a versatile rifle and cartridge combination. Many have chosen it because of it's versatility.
Basic Load Data for the 416 B&M