I've written quite a few posts about Hornady Sub-X. It's shit and you're definitely going to end up wounding animals if you don't make well placed head/neck shots, plus I've had quite a few of them going supersonic, so the worst of all worlds. You may as well use cheaper subsonic ammo if you're going for head shots. On the supersonic side, Hornady FTX are absolutely devastating. No complaints there and I would be happy to use them on smaller deer species. Be aware that much of the 300BLK ammo available isn't designed for hunting, so choose carefully.
Bookmarks