Sierra uses the same core alloy (3% antimony) in the ProHunter and GameKing, the only difference being the boattail. Both work pretty darn well if not carelessly applied (say over 2800 fps impact velocity on deer, 2400 or so on bigger game). I use the 160 GameKing a lot in the 7x57 on deer-sized game, and have yet to recover one.
At least one other bullet company uses a MUCH softer core in their boattail bullets, which is perhaps one reason boattails have a reputation for coming apart. But I did an analysis of hundreds of bullets shot into big game and found that the common belief that boattails shed their cores more easily than flat bases is pretty much myth. Or at least it was in my sample of several hundred bullets. In fact, more flat-bases separated than boattails, on a percentage basis.
