feed opening

magazine feed-piece opening

belt feed pawl (belt-feed pawl)

belt-feed pawl pin / belt feed pawl pin

belt feed pawl spring / belt-feed pawl spring

belt feed lever pivot spring / belt-feed lever pivot spring

feed block slide (feed-block-actuating slide)

create an opening

high altitude-high opening (HAHO)

high altitude-low opening (HALO)

high-altitude low-opening parachute technique (HALO)

firing signals (opening, shifting, ceasing fire)

air intake opening

air inlet opening

belt opening

breech-opening mechanism

breech-opening motor

clear opening

cylinder block inlet opening

front-sight opening

limit of opening fire

frame around opening

valve opening lead

muzzle opening

quick-opening cluster

opening portlight

opening charge

opening elevation

opening line of barrage

opening narrative

opening of hostilities

opening range

opening situation