In the first part of the 17th c. a soldier would have a bandolier of about a dozen wooden bottles slung over his shoulder, each containing one charge of powder and ball. He would also have a powder horn for priming his matchlock musket or arquebus , and some more balls in a leather pouch- so he could keep loading and firing , but not as fast. As he would commence firing at relatively close range- around 100 meters- it was not unlikely that after a few volleys the opposing force would engage and the musketeer would be wielding his gun like a club, next to the pikemen.

Sometime after the 30 Years War and the advent of the flintlock musket the bandolier was replaced by a large leather cartridge box, worn at the belt, which contained around 20 paper-wrapped cartridges- the paper would be run down the barrel on top of the ball, to keep it from rolling out. That box had a large flap over it that was designed to shed water. But still: black powder is hygroscopic ,will greedily absorb water from the air. Even if the cartridges were dry, the soldier would still have to be loading loose powder into the barrel, and priming the pan with loose powder. This would not be easy to do in the rain, and of course if the gun was loaded with damp powder and wouldn't fire, the charge had to be pulled- which was not done quickly. Commanders who wanted to fight their armies in the rain would have to know these risks.