What ballistics can you get with a .400 Whelen...
It's basically a straight wall cartridge running at high pressure with a case 2.5" long and the cartridge 3.33" long. Bullets to SD of 0.34 are readily available.
There's an analogous cartridge--one that fits the same description--from which you can gauge the ballistics: the .458 Win. With the same SD (ie. 500 gn bullets), Hodgdon's data shows you get 2150 fps. The .400, then, should be able to send its 400 gn to the same 2150 fps, matching the old 450/400.
It would be a very versatile cartridge. The 400 gn could reasonably be used on the heaviest game. With Trail Boss and .41 Mag pistol bullets, it's a mild recoiling deer rifle.
Like Docbill, I've thought a Rem 7600 in this would be a pretty spiffy rifle, but I'm not much for recoil any more, so I never got around to trying it.
