On firing, the gas presses the ring
firmly against the flat plate, and renders escape impossible as long as
the surfaces remain uninjured. When they become worn, the ring and
plate can be exchanged in a few minutes. Mr. Vavasseur, of Southwark,
constructs his guns on a very similar plan. In the French guns, and our
modern ones, the bore is continued to the rear extremity of the piece,
the breech end forming an intermittent screw, that is, a screw having
the threads intermittently left and slotted away. The breech block has
a similarly cut screw on it, so that when the slots in the block
correspond with the untouched threads in the gun, the block can be
pushed straight in, and the threads made to engage by part of a
revolution. In the French Marine the escape of gas is stopped very much
as in Krupp's system; a Broadwell ring is let into a recess in the end
of the bore, and a plate on the face of the breech-block abuts against
it.
In the French land service the escape is sealed in quite a different
manner. A stalk passes through the breech-block, its foot being secured
on the exterior. The stalk has a mushroom-shaped head projecting into
the bore.
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