I killed my first turkey in '79 using a .45 caliber Bobb Watts longrifle...I called him in using a wingbone call that I had made...My load was 40 grains FFF, and I held for where the wing meets the body, didn't tear up too much meat....Since then I made me a .54 flinter for deer and rebarreled the .45 to a .40 which should be a dandy turkey caliber, but, I moved back to NC and they won't let us use rifles of any type...
I assume you have a .50 and a .32...I'd go with the .50 and use half you regular charge...That's how I usually set up my deer calibers, I want them to shoot flat to 25-30 yards for squirrels with half a charge and then 1-2 inches high at 50 yards, with a full charge, this puts them dead on at 75 and about and inch low at 100....
Guess I'm saying I'd use about 50 grains in the .50 for turkey...If facing, hit where the neck meets the body, broadside, where the wing meets the body....
Or I could just bring my .40 and show you how its done...