For me to take a neck shot with a muzzleloader, it would have to be with the deer facing directly at me, and even then I would shoot low enough that the bullet's path will take it through the boiler room.
As for a head shot at close range, I feel that a spine shot is a better alternative. Hold high over the lung region and pull the trigger. Miss high, and you've got a clean miss. Miss a little low, and you've still shocked the spine and the deer will be unable to run for long enough for you to put another in him. Miss a lot low, and you just put one through the lungs. Missing left or right will still hit spine, but you don't want to go too far back or you've ruined the backstraps.
Only thing that makes this shot iffy is that it requires a finishing shot, but that's easy enough to do.
I've only taken this shot twice, and both times it was on relaxed deer from a rock steady bench I built into my shooting house (this is actually the same rest I use for benchrest shooting my rifles) at less than 20 yards. I chose the spine shot over the boiler room because the deer were on the edge of a huge field of standing corn and recovery would have been a challenge, to say the least.
