Welin breech block

Welin breech blocks provide obturation for artillery pieces which use separate loading bagged charges and projectiles.

Each step engages with its matching thread cut in the gun breech when inserted and rotated.

These in turn required more time and much greater room to extract and move aside to gain access the gun's chamber to clean and reload it.

The engagement of threads around much more of the circumference of the Welin block allowed it to be shorter for the same total engagement area and strength, it required less than 90 degree rotation to lock the threads, making operation faster than previous designs and possible in much tighter space.

The Welin breech was a single motion screw, allowing it to be operated much faster than previous interrupted-thread breeches,[citation needed] and it became very common on British and American large calibre naval artillery and also field artillery above about 4.5 inches (114 mm).