Flintlocks are designed to function using real black powder. The only substitute that can be used in Flintlocks and works is the Goex Pinnacle powder, which has a much lower flashpoint than the other subs, like Pyrodex. Anyone can order Black Powder from one of the suppliers listed in the links and have it delivered to their homes, usually much cheaper than the cost of the subs.
I can't imagine you wanting to shoot a saboted .44 pistol bullet in a flintlock! That .50 cal. gun will take game with a PRB- certainly any deer you are every like to see. The PRB weighs in at 180 grains, and mushrooms on impact making a hole that is much larger than 60 caliber on most deer. At any distance under 100 yards, it is likely to completely penetrate a deer, leaving a massive primary wound channel, and blood spurting out of both sides of the animal. You can buy short conicals, including the maxi-balls sold by T/C, to shoot in that gun, if you are using it to hunt Elk, Moose, Caribou, or bear, but you won't need anything like a 300 grain bullet in .44 cal. to kill anything with that gun.
I know all the guys are talking about taking 200 yards shots, and I suppose if you are allowed to put modern variable powered scopes on your smokepole in your state, you might get such a shot, and you might just hit the deer. However, even using pistol bullets, the trajectory at those ranges is pretty steep- ie. the bullet is dropping very fast- so unless you have the time to put a laser range finder on the target to tell you exactly how many yards away that deer is, a miss is just as likely with those pistol bullets as with a round ball.
You would have to spend many hours at a range shooting from different positions to simulate hunting conditions before you will have any confidence of making such a long shot! Remember, 200 yards is 600 feet, and that is a long way in anybody's book. Even a high powered scope is not going to show you blades of grass, twigs, small saplings growing between you and that deer's vital area. At 200 yds, the best settings on a scope still leave a pretty wide set of cross hairs, which cover up a lot of the target, and a lot of stuff in between you and the deer.
Those are just some of the reasons those of us who choose to hunt with flintlocks pass on those kinds of shots. It is much more important to get close, and much more satisfying when you do get close and successfully kill the deer with a traditional flintlock.
You are not going to make a .50 cal. T/C Hawkin into a magnum deer rifle, using sbots, and pistol bullets, of any weight- it is already a " Magnum " deer rifle, within the range it was designed to shoot with open sights. The vast majority of deer are still killed at under 50 yards, as the comments made here in the forum by members reporting on their kills will attest. ANy deer killed with a flintlock is a trophy. Once in a blue moon, a hunter with a traditional gun is in the right place at the right time, and is able to kill a Boone and Crockett record book buck. It happens about as often as that kind of thing happens to other deer hunters.
You have to have better things to think about sitting on a bar stool, than trying to make something out of a traditional gun that it isn't. Aren't here any women in the bar?
Good Hunting.
