How much powder should you use in your 50 caliber flintlock?

The exact amount will depend on your gun patch and ball combination and distance you are shooting, and type of gun (pistol, smooth bore musket, rifle, carbine rifle, long rifle etc.) Each gun has it's "sweet spot" that is a powder charge and ball combination that gives consistent results, so you will have to experiment to find it. In my .50 flinter long rifle (42" barrel) I use 64 grains of 3F powder for shooting 50 to 100 yards and 50 grains under 50 yards, in my Hawken style flinter (28"barrel) I use 55 grains for long shots and 45 for short and in the pistol I use 25 grains. Those are target loads, for hunting I am between 75 and 90 grains on both guns, and the pistol is not used for hunting accept as a back up. The best way I have found is to start out with as many grains as the caliber and work from there placing targets at the distances you expect to be shooting. Fire 3 to 5 shots and record your results, increasing the powder charge by 5 grains each set. Keep in mind not to exceed the maximum recommended charge for your gun, and that the key to muzzle loading accuracy in consistency, load the exact same way each time, paying attention to the direction of the weave of your patch and how firmly you pack the load. With some time and patience you will have a tack driver.