I own a Marlin 450 Guidegun, using the Hornady 350gr FN Interlock, on top of 50gr H4198, CCImag primers, Lee factory crimp(heavy) 2180fps. I have used the hornady 350gr fn Interlock, for black bear and German boar hunting, I was successful hunting both using the Hornady 350gr FN, but one thing I did notice, there was no real expansion of the interlock, but it sure had good Penetration on both animals, a good hearty bullet, very tough...In saying this, running them at 1600fps, would be no chance for expansion, unless you hit something very solid, like a shoulder bone, and even at that it may not open up. using the .458 dia, you really don't need much expansion, makes a good hole either way. A good penetrator. Aim small hit small. RAMbo.