A worm is a device used to remove unspent powder bag remnants from a

cannon A cannon is a large- caliber gun classified as a type of artillery, which usually launches a projectile using explosive chemical propellant. Gunpowder ("black powder") was the primary propellant before the invention of smokeless powder ...

or other piece of muzzle-loading field

artillery Artillery is a class of heavy military ranged weapons that launch munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during siege ...

. It usually took the form of a double corkscrew-shaped piece of iron on the end of a long pole that could be twisted down the barrel to pick up any debris left over from the previous firing of the weapon. It was usually turned twice before being pulled out.

References

Cannon {{artillery-stub