The military was at least recommending powder horns and fine 'pistol powder' as early as 1758, and for sound reasons:It is my understanding that there were no priming horns & no separate grades of gunpowder used for priming in the 18th century.
Extract from a letter from Major George Scott, 40th Foot, CO of the Light Infantry Battalion on the February, 1758, Louisbourg expedition, to Lord Loudoun, CIC in America. This letter refers to kit he is recommending for rangers and light troops:
“The powder horn recommended carrying pistol powder with its more combustible grain. Easily ready to hand and slung off the left shoulder under the right arm pit, the horn is a quicker and more convenient way of priming one’s musket, and is not subject to burn powder [flash in the pan] or miss fire. It also prevents the most common fault which men are subject to in time of action Vis, that of spilling 1/2 of their cartridge of powder and at times more in priming and shutting their pans. The result of such nervousness or sloppiness on the part of a soldier in action means that the ball will not be sent with 1/2 the force it is intended or anything near the distance it aught to go.”
Spence