Part 4 (1/2)
Pedreros (fig. 23c) were comparatively light. The foundryman used only half the metal he would put into a culverin, for the stone projectile weighed only a third as much as an iron ball of the same size, and the bore walls could therefore be comparatively thin. They were made in calibers up to 50-pounders. There was a chamber for the powder charge and little danger of the gun's bursting, unless a foolhardy fellow loaded it with an iron ball. The wall thicknesses of this gun are shown in Figure 24, where the inner circle represents the diameter of the chamber, the next arc the bore caliber, and the outer lines the respective diameters at chase, trunnions, and vent.
[Ill.u.s.tration: Figure 24--HOW MUCH METAL WAS IN EARLY GUNS? The charts compare the wall diameters of sixteenth-seventeenth century types. The center circle represents the bore, while the three outer arcs show the relative thickness of the bore wall at (1) the smallest diameter of the chase, (2) at the trunnions, and (3) at the vent. The small arc inside the bore indicates the powder chamber found in the pedrero and mortar.]
Mortars (fig. 23d) were excellent for ”putting great fear and terror in the souls of the besieged.” Every night the mortars would play upon the town: ”it keeps them in constant turmoil, due to the thought that some ball will fall upon their house.” Mortars were designed like pedreros, except much shorter. The convenient way to charge them was with _saquillos_ (small bags) of powder. ”They require,” said Collado, ”a larger mouthful than any other pieces.”
Just as children range from slight to stocky in the same family, there are light, medium, or heavy guns--all bearing the same family name.
The difference lies in how the piece was ”fortified”; that is, how thick the founder cast the bore walls. The English language has inelegantly descriptive terms for the three degrees of ”fortification”: (1) b.a.s.t.a.r.d, (2) legitimate, and (3) double-fortified. The thicker-walled guns used more powder. Spanish double-fortified culverins were charged with the full weight of the ball in powder; four-fifths that amount went into the legitimate, and only two-thirds for the b.a.s.t.a.r.d culverin. In a short culverin (say, 24 calibers long instead of 30), the gunner used 24/30 of a standard charge.
The yardstick for fortifying a gun was its caliber. In a legitimate culverin of 6-inch caliber, for instance, the bore wall at the vent might be one caliber (16/16 of the bore diameter) or 6 inches thick; at the trunnions it would be 10/16 or 4-1/8 inches, and 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
b.a.s.t.a.r.d 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.
[Ill.u.s.tration: 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 lacked the defects of the chambered pieces. A 60-pounder reinforced cannon fired a convenient 55-pound ball, was easy to move, load, and clean, and held up well under any kind of service. It cooled quickly. Either cannon powder or fine powder (up to two-thirds the ball's weight) could be used in it.
Reinforced cannon were an important factor in any enterprise, as King Philip's famed ”Twelve Apostles” proved during the Flanders wars.
_Fortification of sixteenth and seventeenth century guns_
------------------------+-------------------------+--------------------- Thickness of bore wall in 8ths of the caliber Spanish Guns +-------+---------+-------+ English guns Vent Trunnions Chase ------------------------+-------+---------+-------+---------------------
Light cannon; bell-chambered cannon 6 4-1/2 2-1/2 b.a.s.t.a.r.d cannon.
Demicannon 6 5 3 Common cannon; common siege cannon 7 5 3-1/2 Light culverin; common battering cannon 7 5 3 b.a.s.t.a.r.d culverin; legitimate cannon.
Common culverin; reinforced cannon 8 5-1/2 3-1/2 Legitimate culverin; double-fortified cannon.
Legitimate culverin 9 6-1/2 4 Double-fortified culverin.
Cast-iron cannon 10 8 5 Pasavolante 11-1/2 8-1/2 5-1/2 ------------------------+-------+---------+-------+---------------------
While there was little real progress in mobility until the days of Gustavus Adolphus, the wheeled artillery carriage seems to have been invented by the Venetians in the fifteenth century. The essential parts of the design were early established: two large, heavy cheeks or side pieces set on an axle and connected by transoms. The gun was cradled between the cheeks, the rear ends of which formed a ”trail”
for stabilizing and maneuvering the piece.
Wheels were perhaps the greatest problem. As early as the 1500's carpenters and wheelwrights were debating whether dished wheels were best. ”They say,” reported Collado, ”that the [dished] wheel will never twist when the artillery is on the march. Others say that a wheel with spokes angled beyond the cask cannot carry the weight of the piece without twisting the spoke, so the wheel does not last long.
I am of the same opinion, for it is certain that a perpendicular wheel will suffer more weight than the other. The defect of twisting under the pieces when on the march will be remedied by making the cart a little wider than usual.” However, advocates of the dished wheel finally won.
SMOOTHBORES OF THE LATER PERIOD
From the guns of Queen Elizabeth's time came the 6-, 9-, 12-, 18-, 24-, 32-, and 42-pounder cla.s.sifications adopted by Cromwell's government and used by the English well through the eighteenth century. On the Continent, during much of this period, the French were acknowledged leaders. Louis XIV (1643-1715) brought several foreign guns into his ordnance, standardizing a set of calibers (4-, 8-, 12-, 16-, 24-, 32-, and 48-pounders) quite different from Henry II's in the previous century.