I made a lego hand cannon when i was bored(you can reload like most of handcannons in destiny(if you want too see write in comment) and it shoots but not very well) :
Death Star Cannon 75246 | Star Wars™ | Buy online at the Official LEGO® Shop US
Lego Dark “Pearl” Gray Shooting Cannon W/ Red Base & Gray Wheels | eBay
LEGO IDEAS - Cannon Firing Crew
LEGO Cannons Compared (Firing vs Non-Firing) - YouTube