I agree the .416 Beartooth is very close, but to me the reason for building the .416 on the .450 case would be the same as the reason Marlin did it, the belt longer than a conventional magnum. With any wildcat built on a shortened .458 case (or .375 H&H to be proper) there is a very real risk someone will load that round into a small caliber magnum and fire it. With the belt providing headspace the round will fire and you can imagine the pressure that pushing a .416 bullet thru say a 7mm bore would produce.