Selecting one, I jammed it into the chamber and closed the breech block.

However, the unique feature is the use of a locking breech block within the slide.

It would eventually become difficult to move the breech block and reload the rifle.

If the threads were not cut away, locking the breech block would require several turns.

The M102 howitzer has this type of breech block.

A corresponding modification was made to the rear corners of the breech block.

The butt was cracked through and the breech block jammed solid.

The breech block closes the chamber behind the powder case.

In later models the A-19 gun was modified to have a semi-automatic breech block.

You see, the breech block really stands a great part of the strain.