Grantville Gazette 45 gg-45

by Paula Goodlett

  Even so, there were skeptics. After the Battle of Lissa (1866, Austria vs. Italy), Tegethoff, the Austrian commander, commented, "the lack of results on the part of the enemy have shown that smoothbore guns on the sea have much more value than a rifled one, since a rifle requires for best results at long range a still position, difficult to find on the sea." (Greene 254).

  The driving force for the adoption of rifled guns appears to have been not so much increasing effective range but that they could fire an elongated shell, thus one carrying more explosive for a given caliber. (Colomb 340ff). But it took perhaps two decades to perfect heavy rifled cannon (Bell 44; Lewis 65), and Dahlgren smoothbore-armed Civil War vintage monitors were placed on coastal defense duty during the Spanish-American War.

  In order to apply spin to the projectile, it must somehow engage the rifling. With small arms, the bullet could be made of lead, which is malleable. There were two problems with making artillery projectiles out of lead. The first was that lead was expensive, and the second was that lead, being soft, would foul the inside of the barrel.

  A number of expedients were tested in the nineteenth century. A lead coating on the projectile was introduced by Baron Warhendorff in the 1840s. (Kinard 222). That wouldn't be as expensive as making the whole thing out of lead, but fouling would still be a problem. The British nonetheless used this system with breech loaders.

  Whitworth and Lancaster made projectiles with twisted side faces to match a twisted bore, hexagonal for Whitworth, oval for Lancaster. When mass produced, the rounds tended to jam in the bore. The Confederates used some Whitworth rifles.

  For rifled muzzle loaders, one had to provide sufficient windage that the projectile could still be rammed down the barrel. One solution (Armstrong, 1854) was to provide the projectiles with studs to engage the grooves of the rifling. The engagement is reliable but the projectile must be studded to match the twist in a particular gun, and the gun cannot have increasing twist. Also, the grooves must be wide and deep to accommodate the studs, and that weakens the gun, whereas the studs increase air resistance to the projectile. (Bruff 303).

  If the studs were taller than the depth of the grooves, there would be a clearance between the main body of the projectile and the lands (the uncut portions of the bore between the grooves). (Woolwich 182). Unfortunately, if the studs have clearance, and there's no gas check, then gas escapes and damages the bore.

  It was discovered that the copper gas check I mentioned earlier not only reduced the gas loss from windage, it also engaged the rifling. It was used in rifled muzzle loaders, but it was found advantageous to make the grooves shallower and more numerous than in a breech loader.

  However, the most successful ploy was to place "a copper 'driving band' into a groove cut around the body of the projectile." (EB11/Ammunition). While the basic concept is in Grantville Literature, there are some serious engineering considerations. We have to figure out what material to make it out of, how thick and long it should be, whether to have one long band or several short ones, where on the projectile body to place it, and how to secure it there. The choices we make, in turn, determine how well it engages the rifling, how much wear it imposes on the bore, and the aerodynamic characteristics of the projectile. (See 1922 EB/ "Ammunition").

  In canon, each of the USE ironclads is equipped with four 10"x 12 rifled muzzleloaders and six rifled 8" x 4 carronades. The ten-inchers fire studded shells. (1633 Chap. 4; 1634: TBW Chap. 38)

  Smoothbores may be converted into rifles by insertion of a wrought iron tube (reducing the caliber, probably by about two inches) after reaming out the old bore to match the outer dimension of the tube.

  With spherical shot, you impart spin by creating friction between the ball and barrel, either by stuffing a patch between the two, or giving the ball a coating of lead or other soft metal. The patch, typically cloth or leather, is placed on the mouth of the rifle and the ball is placed over it. The ball is then stuffed down. Besides promoting spin by filling the grooves, the patch helped prevent the ball from riding back upbore before firing, thus separating bullet and powder, and avoids transfer of lead from ball to barrel. (Fadala 94ff).

  There will no doubt be heated arguments with regard to the fine points of rifling: the number of grooves, the degree of twist, and the shape of the groove.

  Rifling does increase the friction between the projectile and the barrel, and this can reduce muzzle velocity and also generate heat and quicken the erosion of the barrel. This has led to proposal of hybrid guns, with either a smoothbore breech and a rifled muzzle (Alsop, US Patent 37193) or the reverse (A'Costa 4660312; Amspacker H1365). However, a more conventional solution to unacceptable friction has been to put the projectile into a plastic-sabot (see part 4) so that the friction is plastic-metal rather than metal-metal.

  Gunmetal

  Wrought iron. Until the sixteenth century, cannon were forged; the tubes were built up from longitudinal metal strips, and these were held together by metal hoops. (This was blacksmith work, and blacksmith Marthinus Ras made three muzzle loading 6.5 pounder cannon by this ancient method during the Boer War.)

  The hooped bombard of the fourteenth century was made of wrought iron. But by mid-sixteenth century, the large wrought iron pieces were only found on small merchant ships and in peripheral fortifications. Small wrought iron swivel guns may still exist in our period.

  Bronze first appeared in hooped bombards in the early-fifteenth century. In the sixteenth century, it was the dominant gun metal. I should note that the British navy has the incredibly annoying habit of identifying bronze guns as "brass." Brass is a copper-zinc alloy, bronze is copper-tin; in the sixteenth century, the preferred ratio was 90–10. (Guilmartin 307). While tough, bronze is soft and thus subject to abrasion, especially if the barrel is hot from repeated firing. Bronze also suffered from a lack of homogeneity. When cooling, the tin has a tendency to separate from the copper, causing white blotches called "tin spots" which are eaten away by the powder gas. (Ord1880,76ff).

  There were essentially four kinds of bronze guns: pedreros, cannons, culverins and mortars. Pedreros are stone-throwers and because of the relatively low density of stone, they typically were of large caliber (12–50 pounders for sea service, up to 1000 pounders for land sieges), with short barrels (4–8 times caliber) and a reduced diameter (1/2 to 1/3 caliber) powder chamber. The Ottomans cast them muzzle down.

  Both cannon and culverins fired cast iron cannonballs, but the culverins had long (18–40 times caliber, mostly 25+) unchambered bores, whereas the cannon had shorter (15–28 calibers, mostly 15–20) bores; early cannon often had reduced diameter powder chambers. (Guilmartin 175ff; Meide; Hoskins 119ff).

  Mortars were designed to shoot at high angle trajectories, and were mostly used as siege weapons. A ship could carry mortars that could be landed and used to strike a position that was out of reach (because of shoals or batteries) of the ship's guns. Mortars had lengths of 1.5–3 calibers.

  Cast iron is iron with more than 2 % carbon. Depending on how the carbon is combined, it may be called white (hard but brittle) or grey (softer but tougher, preferred for cannon). Cast iron guns appeared around 1543. Over the course of the seventeenth century, cast iron gradually supplanted bronze as cannon material. This was despite bronze's advantages; it didn't rust, it was easier to cast ("iron had a tendency to harden before all of it could be poured into the mould"-Lavery 84), it could be recast without loss of strength, and bronze cannon could always be made lighter than cast iron guns of equal strength. For example, in 1742, a British navy 32-9.5 weighed 6048 pounds in bronze and 6384 in cast iron, and a 42–10 was 7392 pounds in bronze and a walloping 8400 in iron. (Meide).

  Nineteenth-century cast iron had a lower yield and breaking strength than bronze (Ord1800, 189), so additional metal was used, preferably at the breech. (Hazlett 82). While a more uniform cast iron could be made in the early-nineteenth century, thanks to improvements in iron-making (coke replacing charcoal, steam replacing water
power)(Morriss 188-9), it remained unpredictably brittle (light field pieces were especially prone to bursting-Hazlett 220), thanks presumably to variations in the nonferrous constituents (phosphorus, sulfur, etc.). In the Civil War era, Rodman wrote, "we are at present far from possessing a praactical knowledge of the properties of cast iron in its application to gunfounding." (Wertime 164) and Cooke (53) made a similar complaint in 1880.

  Unfortunately, bronze cannon were much more expensive-initially three- or four-fold; eight-fold by the 1670s (Unger 149; Lavery 84). This was the result of a decrease in the price of cast iron; bronze prices were stable. Consequently, bronze guns sometimes remained in service for more than a century-Rodger 215. (But even iron guns were very expensive and were kept in active service as long as possible-Glete 77.) Wrought iron reappeared as a reinforcing element in the mid-nineteenth century; in 1880 it was 2–3 times as expensive as cast iron. (Cooke 654).

  As time passed, first the lighter guns were made from cast iron, then all guns save those on "prestige" ships (flagships and royal yachts) went ferrous. (Glete 24ff). The 42-pounder was first cast in iron in 1657, but 30 % of culverins were still bronze in 1660 (Nelson).

  Even on first class warships, bronze was pretty much no longer on deck by the 1770s. (Although the British navy still had some bronze mortars in the 1860s.) Bronze continued to be used as a gun metal for field artillery in the nineteenth century, as late as the Crimean War and American Civil War, no doubt because of its weight advantage. These included a 14-pounder James rifle. Unfortunately, it wasn't suitable for rifled weapons. Since bronze is softer than iron, and the rifling exposed more in tin spots, "repeated firings rapidly wore down the lands, thus making the pieces increasingly inaccurate." (Kinard 193; Hazlett 52). Even for smoothbores, the softness and the tin spots were problematic when challenged by the heavier projectiles and more powerful charges of the nineteenth century.

  In the 1870s, the Italians and French found that guns cast from phosphor bronze (stronger, more homogeneous metal) were superior to those made using ordinary bronze, but concluded that the advantage was too small; the phosphorus had to be added in exact proportions and was "unstable." So-called "bronze steel," an ordinary bronze cast under pressure while chilling the interior, and subsequently forged cold, was also considered, but eclipsed by steel. (Ord1880, 77, 187).

  Cast steel. Steel is potentially superior to cast iron, and to wrought iron and bronze, but it is quite difficult to cast without hidden defects (Kinard 230). Krupp cast his first steel cannon in 1847 (Krause 59). There was only limited use of cast steel rifled cannon (3" Sawyer) in the ACW.

  By the l890s, ordinary steel was replaced by nickel steel. (Krooth 89).

  Cannon Manufacture

  Hollow casting. In the early-seventeenth century, muzzle-loading iron cannon were cast as single hollow blocks. Making the mold was tricky. In essence, there were two clay molds, a hollow one for the exterior and a solid one (core) for the interior. (Hall, 11ff; Fisher).

  The hollow mold was built up over a pattern made of wood, rope, clay and a friable material like horse dung; the pattern defined the desired shape of the cannon interior. The pattern was coated with a release material, such as an ash-fat mixture or a wax, so the actual mold material wouldn't stick. This mold material was also clay-based, and might be reinforced with rope or animal hair. The mold was reinforced with metal straps, the pattern was carefully removed from its interior, and the mold was baked. The core mold of course was simpler to make.

  The complete mold was lowered into a pit, muzzle up. Note that the interior (core) mold had to be held centered inside the larger mold by a metal spacer (cruzeta; chaplets), which would become part of the gun. In general, this didn't work out perfectly, the core would shift so the bore wouldn't be quite straight. (WeirML, 132).

  The pit was filled with earth so as to hold the mold upright, a "feeding head" (riser) was attached, and the molten metal was poured into it. The latter had to have the right fluidity to properly fill the mold. Once the metal had cooled and solidified, the mold was broken so the casting could be removed. That meant that no two cannon could be identical.

  The cannon was then finished off; the most important finishing steps were cutting off the riser, and reaming out the cast bore so that it had a smoother surface. Diego Prado y Tovar (1603) described a machine, possibly driven by animal power, for accomplishing this, However, the drilling was vertical, with the cannon suspended and slowly lowered over the drill. Note that the machine was merely finishing a hollow casting. Indeed, hollow casting is plainly described in Mieth, A New Description of Artillery (Frankfurt 1684); chapter V discusses the cruzeta (Rainer Prem transl.). Bores were cast to the diameter of the shot and drilled out to the added diameter of the windage. (Hoskins 43).

  Clay molds are criticized in 1634: TBW, Chapter 38: "Clay had a very low porosity, which meant that air bubbles in the molten iron were often unable to escape when the guns were cast and, instead, formed dangerous cavities and weak points in the finished guns." The gun barrels of the USE ironclads used in the Baltic War were fabricated by sandcasting. "Sand was far more porous, which made for much stronger, tougher artillery pieces." Historically, sand molds were introduced in Britain about 1750. (Lavery 84).

  Another problem was intrinsic to the vertical casting method; since the bottom (breech) was under greater pressure than the top, and also better insulated, it would have been the last to solidify, and therefore tin would have migrated downward. The muzzles were thus only 3–5 % tin, resulting in brittleness, which was compensated for by flaring the muzzle.(Guilmartin).

  There were other modest improvements over the eighteenth century. In Britain, these included providing full-size drawings to the gun founders (1716) and using copper rather than wood cores.

  We may deduce the improvement in tolerances by examining the weight variation of the pieces. "In 1665, guns from a single batch of 9ft demi-cannon varied from 44 to 62cwt, those of 8.5 feet from 43 to 47, and culverins of 10ft varied from 40 to 46 cwt." (83). In contrast, the 32-pounders surveyed in 1803 -6 were 55–57 cwt. (84).

  Solid Casting. Over the period 1715 -45, Johann Maritz developed a new fabrication method. The cannon was cast solid, breech down, and then the bore was drilled out horizontally. The casting itself was much as in prior times, except that the core mold was no longer required. Boring itself, using an animal- or water-powered machine, took several days. (Kimpton). One curious aspect of the process is that it was the cannon that was rotated, the bit remaining stationary. (Alder 42). Solid casting was adopted in Britain in 1776 (Lavery 84).

  Hot Blast. In the 1830s, American gunfounders attempted to cast iron by the more economical "hot blast" method, resulting in a disastrous loss of strength. At West Point foundry, 68.5 % of those cast by cold blast (1826–1834) were deemed "first class," compared to 4.02 % of those produced (1835 -39) by hot blast. (Hazlett 36, 42).

  Rodman Guns. These were hollow cast, with a trick; the core was itself hollow, in fact, two concentric tubes, and was cooled with pumped water while the molten iron was poured in around it. The metal would thus cool inside out, pre-stressing it in a desirable way. (Wikipedia/Rodman_Gun).

  Built-Up Construction. The 1855 Griffen "Ordnance Rifle," a 10-pounder cannon with a 3 inch rifled bore, was built up by welding wrought iron bands together around a mandrel, boring, and rifling. (Kinard 192), or by building up a mandrel with welded iron rods and then winding several bars in spiral fashion about it (Hazlett 121). Note its similarities to the ancient bombard, in that it was "built up" from wrought iron! However, it is important to note that instead of forging the iron with a hammer-as was done with the 1844 "Peacemaker," which burst and killed two cabinet members-Griffen forged his iron rods in a rolling mill.

  There was also the British Armstrong gun. This went through several permutations. In one, wrought iron bars were twisted into spirals and welded on their edges to form the barrel. (Tennent 106). In some cases the twisted coils were themselves s
hrunk onto an inner tube of mild steel. (Morgan xvi).

  Wrought iron's advantage was that it was four times stronger than cast iron, and thus able to help resist the higher internal stresses (the result of the reduced windage) of a rifled gun. Saving manufacturing cost and time, Parrott shrunk a wrought iron reinforcing hoop onto the breech of a rifled barrel cast in the usual way. However, "large Parrott rifles had the worst record of any Union cannon for premature bursting. Of 110 large caliber Union cannon that cracked or burst in action during the war, 83 were Parrotts. " After the first 1864 assault on Wilmington, Admiral Porter declared that the guns were "calculated to kill more of our men than those of the enemy." (Bell 8).

  Around the end of the nineteenth century, the British and Japanese made use of wire wound construction. The "A" tube was wrapped multiple times with a high tensile strength wire and then the "B" tube was shrunk over this. (DiGiulian). The ten-inch guns of the new time line's USE Constitution are "wire-wound" (1634: TBW Chap. 38), presumably over a cast tube, but I don't know if a "B" tube was added.

  In the early-twentieth century, heavy naval guns were built-up in hoop-over-tube fashion. The inner tube was placed breech end down in a cold pit, supported by a short mandrel. Heated hoops were placed one by one over the tube and cooled with a water spray, shrinking them onto the tube. (NAVORD. 136).

  Spun Cast Monoblocs. In the 1920s, this was superseded by monobloc construction, made possible by the development of centrifugal spun casting. Despite the name, it typically involved concentric assembly of two or three tubes. Autofrettage was used to permanently deform the tubes in a desirable way. In autofrettage, the tube was pressurized hydraulically, just enough so that the outer limit was at its elastic limit, and then slowly relaxed. This increases the diameter of the bore and there is a permanent strain in the tube which varies from the inside diameter to the outside one.