UPU-210

"Consider the UPU-210 the Negotiator's musclebound, eyepatch-wearing older brother. This beast fires six impact-detonating grenades per round."

The UPU-210 is a grenade launcher in Just Cause 3.

Description
Its a burst fire grenade launcher. It resembles the DP-64 grenade launcher, except the UPU has an older design (with the wooden stock and all).

Modern weapons normally have a plastic, or carbon fiber stock, so the wooden stock indicates the weapons possible age as being more than 3 decades.