Technic Gun Building Blocks, MBKE 1004pcs 98K Blaster Military Gun Model , Swat Military Weapon Model Building Set Compatible with Lego Technic : Amazon.co.uk: Toys & Games
Working Lego Pistol (3 stud wide)
2 Simple Lego Technic Guns - Instructables
LEGO building instructions - PARABELLA Rubber Band Pistol - YouTube