Home » Gun Information » Gun Glossary | Gun Terminology » Submachine Gun Submachine Gun:A submachine gun is a fully automatic (full-auto) firearm that fires pistol ammunition. These firearms are most effective for close-range combat.Some submachine guns are also capable of semi-automatic fire. Share this gun news:Click to share on Facebook (Opens in new window)Click to share on Twitter (Opens in new window)Click to share on Pinterest (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Tumblr (Opens in new window)