d at the
smallest diameter of the chase, 7/16 or 2-5/8 inches. This table
compares the three degrees of fortification used in Spanish culverins:

Wall thickness
in 8ths of caliber
Vent Trunnion Chase

Bastard culverin 7 5 3
Legitimate culverin 8 5-1/2 3-1/2
Double-fortified culverin 9 6-1/2 4

As with culverins, so with cannon. This is Collado's table showing the
fortification for Spanish cannon:

Wall thickness
in 8ths of caliber
Vent Trunnion Chase
Canon sencillo (light cannon) 6 4-1/2 2-1/2
Canon comun (common cannon) 7 5 3-1/2
Canon reforzado (reinforced cannon) 8 5-1/2 3-1/2

Since cast iron was weaker than bronze, the walls of cast-iron pieces
were even thicker than the culverins. Spanish iron guns were founded
with 300 pounds of metal for each pound of the ball, and in lengths
from 18 to 20 calibers. English, Irish, and Swedish iron guns of the
period, Collado noted, had slightly more metal in them than even the
Spaniards recommended.

[Illustration: Figure 25--SIXTEENTH CENTURY CHAMBERED CANNON.
a--"Bell-chambered" demicannon, b--Chambered demicannon.]

Another way the designers tried to gain strength without loading the
gun with metal was by using a powder chamber. A chambered cannon (fig.
25b) might be fortified like either the light or the common cannon,
but it would have a cylindrical chamber about two-thirds of a caliber
in diameter and four calibers long. It was not always easy, however,
to get the powder into the chamber. Collado reported that many a good
artillerist dumped the powder almost in the middle of the gun. When
his ladle hit the mouth of the chamber, he thought he was at the
bottom of the bore! The cylindrical chamber was somewhat improved by a
cone-shaped taper, which the Spaniards called _encampanado_ or
"bell-chambered." A _canon encampanado_ (fig. 25a) was a good
long-range gun, strong, yet light. But it was hard to cut a ladle for
the long, tapered chamber.

Of all these guns, the reinforced cannon was one of the best. Since it
had almost as much metal as a culverin, it lack