Trench gun model 1897.

TYPES OF CARTRIDGES:

00 Buck - standard fraction
A bullet is a single heavy projectile
Frag - Explosive Projectile
Magnum is a version of a shot with high damage and a slightly larger spread.
Rocket - a group of rockets (realism)
A nuclear bomb is one big bang

HOW TO USE:

Find "Trench" in the tools menu. Press LMB to shoot. RMB once to pull the pump back, then again to push it forward. R - recharge. Use MMB to switch cartridge types. The options are on the Mods manager page.

variants:

Unlimited number of cartridges (cartridges do not run out)
No recoil