several jackets are put on, one over the other, to make the gun
stronger.

If you have ever seen a blacksmith put a tire on a wheel you
will understand what I mean. The tire is heated, and this expands
it, or makes it larger. It is put on hot, and when it cools it
shrinks, getting smaller, and gripping the rim of the wheel in a
strong embrace. That is what the jackets of steel do to the big
guns.

A big rifled cannon is loaded from the rear, or breech, just as
is a breech-loading shotgun or rifle. That is, the cannon is
opened at the back and the projectile is put in by means of a
derrick, for often the projectiles weigh a thousand pounds or
more. Next comes the powder--hundreds of pounds of it--and then
it is necessary to close the breech.

The breech block does this. That block is a ponderous piece of
steel, quite complicated, and it swings on a hinge fastened to
one side of the rear of the gun. Once it is swung back into
place, it is made fast by means of screw threads, wedges or in
whatever way the inventor of the gun deems best.

The breech block must be very strong, and held firmly in place,
or the terrific force of the powder would blow it out, wreck the
gun and kill those behind it. You see, the breech block really
stands a great part of the strain. The powder is between it and
the projectile, and there is a sort of warfare to see which will
give way--the projectile or the block. In most cases the
projectile gracefully bows, so to speak, and skips out of the