The Sheriff Spas 12.
 
Around 100 or so were made in total (never seen any documentation of actual numbers), with half being a full-auto type, and the other half being the more desirable semi-auto version. Both utilise a "Push Valve" system.
 
BBs are fed through a tube magazine system where the gas tube is., with an internal magazine capacity of approximately 40bbs.
 
The heat shield, stock and hook are made of steel, as you can tell by the "patina".
 
The trigger guard is cracked, but doesn't affect use. It's a common Sheriff Spas 12 thing.
 
A working version, of the most desirable model of the rarest production airsoft shotgun in existence.