The Gevär M1815 is a musket. It is chambered in Medium ammo.
It can dispatch most zombies, as well as any player, in one hit. It has the longest reload time of any weapon in the game (tied with Övergeväret). It holds just one shot as is common with most muskets.
Gevär M1805 can be most commonly found on the highest points of the Tower town and the Ruin town, also sometimes (quite rarely) appears in houses of these towns, in the Rollercoaster town and in the Cylinders.