Home made 12 gauge shotgun.
This one uses short recoil mechanism to operate. (luger-style toggle action)
Trigger group is very simple, similar to the ones found in many handguns, and this time safety can be engaged while hammer isn't cocked.
To shoot:
1. Put the shells into the magazine (integral, non detachable, 3 shells capacity) from the top. (like in kar. 98)
2. Disengage the bolt lock (either pull the bolt all the way back and let it go, or pull the bolt release button down)
3. Disengage the safety.
4. Pull the trigger, or push the [return/enter] key. (semi-auto only)
5. Bolt should lock back after the last shell was fired.
Red shell = buckshot
Green shell = birdshot
White shell = rifled slug
Thanks for DualDesertEagle for instructional vid.