Слово "breech". Англо-русский словарь Мюллера

I stopped, and, picking a cartridge from my pocket, I opened the breech of my gun.

Hornblower took out the tampion and went round to the breech; he twirled the elevating screw until his eye told him that the gun was at the maximum elevation at which it could be run out. He cocked the lock, and then, crouching over the gun so that the shadow of his body cut off the sunlight, jerked the lanyard.