The term 'PART OF A GUN' can be broken down into three crossword solutions: BREECH (6 letters), SIGHT (5 letters), and FIRINGPIN (9 letters). The BREECH is the back end of a gun barrel, where the ammunition is loaded. The SIGHT is the device used to aim the gun, usually located at the top of the gun. The firing pin is the part of the gun that strikes the primer of the cartridge, causing it to ignite and fire the bullet.