A sighting device, usually a disk or segment with a central peephole, so designed to fit in the breech end of the gun tube for the purpose of aligning the sights with the gun.
NSN 6135-01-355-8917
NSN 6645-01-350-3138
NSN 6650-00-295-1713
NSN 5910-01-461-3409
NSN 7035-01-647-9698
NSN 6320-00-450-7014
NSN 5975-01-649-1452
NSN 5999-00-827-5761
NSN 5996-01-190-5160
NSN 5935-01-193-1505
NSN 6320-01-246-4390
NSN 5945-00-386-9304