Hi Regulis7,
I have a T/C White Mountain Carbine with a 21" barrel. It does have a fast twist, I think it's 1 in 32? Anyway, I generally shoot Goex 3F blackpowder in it. I'm just guessing that the FFFg is quicker and it seems to shoot a little harder. Anyway, with a short barrel, it might be an idea to try FFFg? (Remember to reduce the load 15% or so below what would be safe with FFg.)
Several years ago, when I was first trying to figure out all of this BP "stuff", I read everything I could find about 50 caliber Roundball, blackpowder, whitetail deer loads. I actually kept a notepad and tallied up dozens and dozens of fellows' recommended "deer loads" for the 50 caliber roundball.
What I tallied up was that a few guys shoot 65 grains, a fair number more shoot 70 grains. Lots of the fellows shoot 75 or 80 grains of Goex FFg. 75 and 80 were far and away the most commonly preferred loads. Only a few shot 90 grains, and when you got to the fellows that shot 100 or higher, they were usually the sabot and conical shooters, which isn't what we're talking about.
Myself, my rifle shoots equally well with 70, 75, or 80 grains. I shoot 80 grains for Whitetail which is probably too much. My rationale is that I would prefer to shoot an exit hole to get a better blood trail. Honestly, a 60 or 65 grain load of Goex FFg would definitely kill the deer, but without an exit hole, you won't get as much of a blood trail, especially with a high lung hit. This is just my thoughts, your experience may differ, but I've spend quite a few anxious hours looking for a hit deer that didn't go down right away...(with a 243 Winchester during my "previous life" with Centerfires.)
Regards to all,
Ironsights Jerry.