There are certain axioms known from experience, which should be
mentioned here. First, the length of the powder chamber should not
be more than three and a half or four times its diameter, if it can
possibly be avoided, because, with longer charges, the inflamed powder
gas is apt to acquire rapid motion, and to set up violent local
pressures. Next, the strength of a heavy gun, as reckoned on the
principle of all the metal being sound and well in bearing, should not
be less than about four times the strain expected.

Again, though there are several opinions as to the best weight of shot
for armor piercing, in proportion to diameter, yet among the most
advanced gun-makers, there is a growing tendency toward increased
weight. The value of w/d cubed, that is, the weight in pounds divided by the
cube of the diameter in inches, as this question is termed, is in the
hands of the Ordnance Committee, and it is to be confidently hoped that
efforts will shortly be made to arrive at a solution. In the meantime,
from about 0.45 to 0.5 appears to be a fairly satisfactory value, and is
adopted for the present.

Lastly, it may be broadly stated, that with suitable powders, a charge
of one-third the weight of the shot demands for most profitable use a
length of bore equal to about twenty-six calibers; a charge equal to
half the weight of the shot should be accommodated with a bore of about
thirty calibers; while a charge of two-thirds the weight of the shot
will be best suited by a bore thirty-five calibers long. Of course, in
each case, greater length of bore will give increased velocity, but it
will be gained at the expense of additional weight, which can be better
utilized elsewhere in the gun.