Bit more info on another--the .416 HOffman..

I did not know you can shoot a 416 Remington in a 416 Hoffman but not vice-versa..

Ripp'

.416 Hoffman
When supplies of .416 Rigby ammo were drying up, due to the demise of Kynoch, many hunters still wanted to use the fantastic .416” bullets, and there were several innovative wildcat designs that kept the bore diameter alive. Many people know about the .416 Remington, which came out in 1988, and has been accepted as a solid performer in the game fields, but the Remington design wasn’t the first. It was an American Professional Hunter in Africa, named George Hoffman, who mated the .375 H&H case with .416” diameter bullets to create the .416 Hoffman. It would produce the same ballistics as the .416 Rigby – a 400-grain bullet at 2,400 fps at the muzzle – but with much less powder, a shorter action and readily available component brass from the .375 H&H. The tradeoff was that it ran at a higher pressure than the huge-cased .416 Rigby, but it still worked very well. Although Remington states that their design is based on the 8mm Remington Magnum case, the designs are so similar that the Hoffman chamber can use .416 Remington ammunition, but not vice versa. Being a huge fan of the .416 Rem. Mag., I’m grateful to Mr. Hoffman for his wildcat, and if you’re looking for something a bit different, talk to your gunsmith about the Hoffman case.