18 Mod 0 uses the same 5.56-millimeter ammunition as the M4 carbine—the ultrashort carbine has a barrel length of just 10.3 inches, making it very compact indeed. The weapon was developed by the ...

Although not technically a submachine gun—the Mk. 18 Mod 0 uses the same 5.56-millimeter ammunition as the M4 carbine—the ultrashort carbine has a barrel length of just 10.3 inches ...