Slugs

Slugs are an uncommon type of ammunition that can be found anywhere. Like Buckshot, they are used by the Double Barrel, Lever Action, and Novuh shotguns. However, unlike buckshot, slugs have very little spread, making them effective at medium range.

Slugs fire only one pellet, but can penetrate through multiple zombies, making them more efficient in spreading damage out among a crowd. Slugs also concentrate all of the shotgun's firepower into one shot, outdoing even the Timberwolf in damage, albeit at a very short range.

Recipe
1 Shells + 2 Bolts = 6 Slugs

Trivia

 * In real life and the current version, slugs only shoot one projectile, whereas in the previous version, they shot two.
 * A plausible explanation for 2 projectiles: You load two bolts into each shell.
 * Unlike buckshot, they don't spawn in farms.