requires several hours to extract and renew the copper ring where worn.

The French land service (_De Bange_) arrangement requires no cutting
into the gun, and no enlargement of the breech screw beyond the size of
the chamber, while it is renewable in a few minutes, merely requiring a
fresh asbestos pad when worn. As regards durability, there is probably
no great difference. I have been informed that with a light gun as many
as 3,000 rounds have been fired with one asbestos pad. But usually
it may be considered that a renewal will be required of the wearing
surfaces of any breech-loader after a number of rounds, varying from six
or seven hundred, with a field gun, to a hundred or a hundred and fifty
with a very heavy gun. Full information is wanting on this point.

Having now decided on the material of which the gun is to be composed,
and the manner in which it is to be constructed, and having, moreover,
settled the knotty point of how it is to be loaded, we come to the
general principles on which a gun is designed. It must not be overlooked
that a gun is a machine which has to perform a certain quantity of work
of a certain definite kind, and, like all other machines, must be formed
specially for its purpose. The motive power is gunpowder, and the
article to be produced is perhaps a hole in an armor-plate, perhaps a
breach in a concealed escarp, or perhaps destructive effect on troops.
These articles are quite distinct, and though all guns are capable of
producing them all to some extent, no gun is capable of producing more
than one in the highest state of excellence.

Thus, for armor piercing, a long pointed bolt, nearly solid, is
required. It must strike with great velocity, and must therefore be
propelled by a very large charge of powder. Hence an armor-piercing gun
should have a large chamber and a comparatively small bore of great