Field Cannon

The field guns were the mobile pieces that could travel with the army and be brought quickly into firing position. They were lighter in weight than any other type of flat trajectory weapon. To achieve this lightness the designers had not only shortened the guns, but thinned down the bore walls. In the eighteenth century, calibers ran from the 3- to the 24-pounder, mounted on comparatively light, two-wheeled carriages. In addition, there was the 1-1/2-pounder (and sometimes the light 3- or 6-pounder) on a "gallopers' carriage—a vehicle with its trail shaped into shafts for the horse. The elevating-screw mechanism was early developed for field guns, although the heavier pieces like the 18- and 24-pounders were still elevated by quoins as late as the early 1800's.

Spanish 4-pounder field carriage
FIGURE 33—SPANISH 4-POUNDER FIELD CARRIAGE (c. 1788). This carriage, designed on the "new method," employed a handscrew instead of a wedge for elevating the piece. a—The handspike was inserted through eye-bolts in the trail. b—The ammunition locker held the cartridges.

In the Castillo collection are parts of early United States field carriages little different from Spanish carriages that held a score of 4-pounders in the long, continuous earthwork parapet surrounding St. Augustine in the eighteenth century. The Spanish mounts were a little more complicated in construction than British or American carriages, but not much. Spanish pyramid-headed nails for securing ironwork were not far different from the diamond- and rose-headed nails of the British artificer.

Each piece of hardware on the carriage had its purpose. Gunner's tools were laid in hooks on the cheeks, There were bolts and rings for the lines when the gun had to be moved by manpower in the field. On the trail transom, pintle plates rimmed the hole that went over the pintle on the limber. Iron reinforced the carriage at weak points or where the wood was subject to wear. Iron axletrees were common by the late 1700's.

For training the field gun, the crew used a special handspike quite different from the garrison handspike. It was a long, round staff, with an iron handle bolted to its head (fig. 33a). The trail transom of the carriage held two eyebolts, into which the foot of the spike was inserted. A lug fitted into an offset in the larger eyebolt so that the spike could not twist. With the handspike socketed in the eyebolts, lifting the trail and laying the gun was easy.

The single-trail carriage (fig. 13) used so much during the middle 1800's was a remarkable simplification of carriage design. It was also essential for guns like the Parrott rifles, since the thick reinforce on the breech of an otherwise slender barrel would not fit the older twin-trail carriage. The single, solid "stock" or trail eliminated transoms, for to the sides of the stock itself were bolted short, high cheeks, humped like a camel to cradle the gun so high that great latitude in elevation was possible. The elevating screw was threaded through a nut in the stocks under the big reinforce of the gun.

While the larger bore siege Parrotts were not noted for long serviceability, Parrott field rifles had very high endurance. As for performance, see the following table:
Ranges of Parrott field rifles (1863)
Caliber Weight
of guns
(pounds)
Type of
projectile
Projectile
weighs
(pounds)
Elevation Range
(yards)
Smoothbore
of same
caliber
10-pounder 890 Shell
..do..
9.75
9.75

20°
2,000
5,000
3-pounder.
20-pounder 1,750 ..do..
..do..
18.75
18.75

15°
2,100
4,440
6-pounder.
30-pounder 4,200 ..do..
..do..
Long shell.
..do..
Hollow shot.
..do..
29.00
29.00
101.00
101.00
80.00
80.00
15°
25°
15°
25°
25°
35°
4,800
6,700
4,790
6,820
7,180
8,453
9-pounder.

Amazingly enough, these ranges were obtained with about the same amount of powder used for the smoothbores of similar caliber: the 10-pounder Parrott used only a pound of powder; the 20-pounder used a two-pound charge; and the 30-pounder, 3-1/4 pounds!


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