a semi-automatic weapon is just any gun you don’t have to cock between shots. so basically every handgun except old-fashioned revolvers are semi-automatic. when describing weapons capable of firing bursts or continuously, you want ‘machine pistol’ for something like an uzi, ‘assault rifle’ for your ak-47′s and such, and ‘machine gun’ for a weapon large enough to be mounted on a tripod or vehicle.
for your reference when writing soldiers and other characters who are familiar with firearms, may i present…
single action revolver:
semi-automatic or semiauto:
machine pistol:
assault rifle or tactical rifle:
shotgun:
machine gun:
happy writing!
(also please can screenwriters stop having everyone cock their weapons to make a menacing noise, it’s tremendously silly. if you don’t have the safety off and a round chambered when you’re aiming it at the bad guy, it might as well have ‘replica’ written on it. joe random civilian might make that mistake, but james bond or bucky barnes or emma peal won’t.)
just moving along like everyone else 