The under-barrel magazine clamp is a clamp for the under-barrel magazine extension to the barrel of the weapon. Designed for use on 12 gauge shotguns. Eliminates the occurrence of the UPM bending to the side or down under its own weight, ensures reliable fastening and guarantees the integrity of the structure. On each side of the clamp the following can be additionally installed: a base for a quick-release QD swivel for attaching a weapon belt; 3-step Picatinny rail for mounting a tactical flashlight or laser laser. The under-barrel magazine clamp is supplied along with fastening elements. Recommended for use with extension cords from 3 cartridges inclusive.