The weak point of the percussion breechloader was breech sealing. Few systems were secure enough to prevent the shooter from being blasted in the face and eyes by hot gas. Unfortunately, fine tolerances and fitting could not stand up to the effects of hot corrosive gases under battle conditions.
Any correction to the sealing problem required balancing two design considerations:
- The tolerances of the breech mechanism must be loose enough to allow the arm to function under conditions of extreme dirt and powder fouling.
- The effective sealing of the breech end of the arm against gas leakage must be accomplished by the very slight expansion of the typically soft brass cartridge (obturation) during firing.
Correcting the tolerance issue was easy. Loose tolerances are a proven approach and design philosophy in firearms manufacture. Parts should be loose enough to prevent the problems that stop a firearm from operating, such as neglect and dirt. The cartridge gas seal function required another leap of technology that will be covered in the evolution of the cartridge.