My state allows Turkey hunting with a muzzleloader. The reg.s read "Muzzleloading firearms" as a turkey weapon, no caliber restrictions for turkey. .44 and larger for deer.
I've killed 2 with a .54 and I just aimed at the body. I was surprised how little damage was done. Some 12 years ago I built a turkey rifle, Haines stock, 38" 'B' weight .40 caliber Rice barrel, Large siler and Davis set triggers. Dark browned steel furniture and a dark stock.
I had several good turkey spots to hunt at that time. First morning out I drove 65 miles, got on a bird gobbling before dawn, got in front of him after flydown and was waiting while he came up the narrow hardwood bottom. Just as he came into the open followed by a smaller bird, I cocked my rifle and the mainspring broke. By the time I got my rifle back in the game I was working 7 days a week. By the next year I had bad knee problems and had lost all my good hunting spots. Have done little turkey hunting since then.
Mainly it is too thick around here to try for many head shots. But if I had a steady prop and a clear shot I would try it. The only other shot is the body, about 1/3 the way up and try to angle the shot so it goes through the vitals and not just the breast.