While not quite as heavy as the AEG Thompson M1A1, the SPAS-12 is a heavyweight replica. The construction is largely plastic with some metal parts, and there are mounting rings for a sling. The SPAS-12 is an extremely durable and well constructed replica.
Propulsion comes from an amazingly powerful spring mechanism.
Each pump of the handle allows you to fire 3 bbs in a single burst, and spread is of course dependent on distance. Both of these features are recreated beautifully, including the three separate points of articulation in the stock. However the stock is optional, so you will want to make sure whether or not the version you are purchasing includes it. One thing that sets AirSoft shotguns apart from their rifle and pistol brethren is the shells. It is loaded into, and removed from, the SPAS-12 through the same port as the real steel.