RE: Which mechanicals at 300fps?
Ken,
At 300fps and a 400gr arrow you don't have to even consider cutting diameter limitations........If I were you I would look at more cutting surface.
Rocket Hammerheads, 3 or 4 blade will be NO PROBLEM, Slammerheads, or 4 blade Sidewinders.
I've used them all and blood trails weren't even an issue because everything fell in sight.
I shot a buck in West Virginia a few seasons ago with a 4 blade Sidewinder.......took one hop, spun in a cirlce and flipped over.[:-] He never made it 10 feet or 3 or 4 seconds (whichever came sooner)
If you have the energy to spare, why not use it?