The Gun - Smoothbore Era 1550-1860
The smooth-bore muzzle-loading (SBML) era to be discussed lasted from the early 1500s until the middle of the 19th century, a period of over 300 years. It does not include the 'think big' projects described in Chapter 4; these were relegated to the garrison/fortification role because they were excessively heavy, extremely difficult to move, had very slow rates of fire, and no two took the same ammunition. Each one was unique; no attempts had been made at standardisation.
|Parts of a SBML gun c. 1800.|
Prior to this date guns had an additional astragal and fillets just forward of the second reinforce ring, and no cascable loop.
As Gunners demanded more mobility two main branches of artillery emerged: field and siege, with the first attempts at some kind of standardisation although the calibres were obviously arbitrary. Each country adopted similar pieces, naming them after snakes, birds of prey etc as was the custom in those days.
Many believe that during the 300 years of the era ordnance underwent virtually no change, ie a gun cast in 1600 was little different from one cast in 1800, but this is not the case. Gunners were never short of ideas for improving their guns, though some ideas were misguided while others were hampered or ignored by hidebound officialdom. We shall examine some of the changes.
Table 1, compiled either during the reign of Henry VIII (1509-47) or early in that of Elizabeth I (1558 - 1603), shows the basic pieces authorised by the former monarch, a pioneer in the production and organisation of artillery in England. Sealed 'patterns'- in this case models - of the pieces were found in his effects after his death. In those days many tradesmen, including gunfounders, could neither read nor write, so it was of little use expecting them to work from drawings or written instructions. Hence they were supplied with models of the guns they were to produce and told to make the finished articles so much larger.
Later lists of ordnance show pieces additional to those shown in Table 1, mostly variations of the basic, some of which no doubt resulted from the method of production outlined above. For example, a bastard piece was one the dimensions of which differed in some way from the pattern. Also, as guns were expected to last for decades there appear old, eldest, ordinary, extraordinary, as well as foreign, ie imported, types. Broadly divided into siege and field, some idea may be gained of their respective employment by a study of Table 2. Both tables refer to English ordnance but types produced in European countries were similar.
In 1665 in England (later in Europe), the old names, eg cannon, culverin, etc, began to be dropped and the guns designated by the weight of shot fired (Table 3). Here we find the first application of a modern basic principle, ie that the projectile is the weapon of the artillery, the gun merely the means of putting it on to the target. The arbitrary progression of calibres by one half or one quarter inch has disappeared. In its place are guns firing projectiles selected for their individual effectiveness, eg the 24-pr fired from a gun of 5.824-inch calibre was found to have the best projectile for all-round siege work.
Note that windage has been changed from one quarter inch for all types to one twentieth the shot diameter - which improved the performance of the smaller guns but not those of 24-pr or larger. ''Rules of thumb'' had still not been entirely discarded. Note also that heavy ''brass'' guns (which were in fact bronze) became obsolescent c1800 because they could not stand high rates of fire as well as those of iron. The lighter field pieces only were retained.
In the beginning gun design was largely by rule of thumb. For example, trunnions were made the same diameter as the calibre, the walls of the piece one calibre thick at the breech and a half calibre at the chase, etc, but no logical reasons could be given for these dimensions, for the designers had no means of gauging bore pressures, muzzle velocity, or strength of materials. Nevertheless, throughput the smooth-bore era much thought continued to be given to improving ordnance, ammunition, and to a much lesser extent, ballistics and gunnery.
We have already seen how the expense of casting was greatly reduced by practical gunmakers' omitting fancy decorations from their guns.
The peculiarities of serpentine, the original gunpowder, have already been explained. As with gun design rule of thumb prevailed, so that at the start of the era - by which time the use of cast iron shot had become general - Gunners made the charge weight the same as that of the shot (in most cases). Where discrepancies occur apparently the guns were shorter than usual and the charges reduced to avoid wastage.
Corned powder, considered upon its introduction to be 30% more powerful than serpentine, was said to have been first produced by the French in 1429. It was first used only in small arms, and does not appear to have been used in ordnance much until later, c1560 in England, by which time guns were strong enough to stand it.
Still using rule of thumb, Gunners continued to make charge weight the same as shot weight - with some very rude shocks when a number of the older guns blew up! Charges of corned powder were therefore reduced to two-thirds those of serpentine with further reductions to about half, especially with the heavier pieces. As experiments with proportions of ingredients and improvements in manufacture proceeded it was found charges could be still further reduced to produce the desired effect. Thus at the end of the smooth bore era they were down to a third the shot weight.
For some two centuries the propellant charge of gunpowder was loaded by means of a ladle designed for the gun in use, but the correct filling of which was left entirely to the judgement of the loader. Therefore the chances of consistent shooting can easily be imagined.
Eventually Gunners realised the problem could be overcome by weighing the charges and enclosing them in bags of some combustible material. Cartridges of linen or paper were being used in England in 1560, and of canvas in 1563. By 1800 flannel began to be employed, followed a little later by serge. The search for a material which would be completely consumed on firing is why so many different materials were tried. Not only did residue from unburnt cartridge bags tend to clog up both bore and vent, but it often remained smouldering after the gun had fired, thus creating a dangerous situation not always corrected by sponging the bore - as not a few one-armed Gunners in those days could testify.
Flannel and serge were the most effective materials but the problem was not entirely solved until the adoption of silk for blank in 1868, and in 1875 for live. Shalloon, a type of coarse silk, was adopted later.
Length and Weight of Guns
With the heavy charges of slow-burning serpentine powder first used, guns had to be long to ensure the propellant charge was all burnt before the shot left the bore. Even then variations in loading conditions and in the quality of the powder caused much of it to be wasted. But long guns were not only difficult to load, they were also heavy. At the start of the era, field and siege artillery were coming into their own with a demand for mobility, for guns which could be easily handled, and which required a minimum number of men and horses to move them. As a result many experiments were carried out; we find for example that a 5.5-in culverin of 28 calibres length in Table 1 by 1646 had been shortened to 22 calibres.
A typical experiment carried out in the early 1700s involved shortening a gun by sawing off a calibre's length at a time while progressively reducing the propellant charge, testing the result by firing the gun at a bank of earth, and measuring the distance penetrated by the shot. Thus we find in 1760 the successor to the 5.5-in culverin, the 5.824-in 24-pr to be 19 calibres in length and achieving a satisfactory penetration with eight pounds of corned powder.
But knowledge gained from tests took many years to be put into effect because pieces of ordnance, especially in the Colonies, were expected to last anything up to a century. In New Zealand we had SBML 24-prs made in 1813-14 on coast defence stations up to at least 1893! Note that the design length of a SBML gun was the distance from the rear of the base ring to the face of the muzzle, not the overall length.
Windage is generally taken to be the difference between the diameters of bore and projectile. Some windage was necessary in SBML guns to avoid dangerous shot start pressures and to enable loading to be easily carried out against accumulation of fouling from poor powder, but excessive windage caused inaccuracy as well as loss of MV. The spherical projectile bounced its way along the bore, the final bounce at the muzzle determining its direction and angle of departure, both of which varied with each round! Once again, for want of any guide, windage was at first arbitrarily set at a quarter inch (6.35 mm) for all natures, an amount still in vogue in the 17th century. Gunners who realised the amount was excessive tried to have it reduced, and quoted the superior performance of the French guns in which the windage was 20% less. However, they were opposed by authorities who ruled that windage must exceed the thickness of the loaders' ladles in order that the gun might be unloaded. When Gunners pointed out that on the rare occasion a gun was found loaded at the end of a practice it might instead be cleared by firing the authorities were outraged. How dare such waste be perpetrated merely for the sake of accuracy! Another excuse for not reducing windage was the liberal tolerances allowed in manufacture not only of bore diameter but also of shot diameter, eg if the bore ended up at the lower figure and the shot at the higher, the powers-that-be argued that windage might be reduced to a dangerous level.
John Muller, in his Treatise of Artillery, 1757, recommended windage be no more than one twenty-fourth the shot diameter, but no one took any notice of him. As the years rolled by, common sense eventually prevailed until by 1828 windage had been reduced to one thirtieth the shot diameter, or less in some cases. Records indicate that while no great increase in range resulted, a significant improvement in accuracy took place.
When trunnions were first invented c1450 they were placed with their axis at right angles to the axis of the bore, the logical place for them one would have thought. Then someone noted that when a gun was fired it tended to rock up and down as in those days it had no elevating gear to hold it in place, or possibly breech preponderance was insufficient. Some mathematical genius thereupon calculated that if the axis of the trunnions was placed at right angles to the bottom of the bore, forces generated by the gun firing would hold the breech down. How right he was. Not only were breeches well and truly held down, for the next 300 years Gunners were plagued by cracked or broken trails on field pieces or beds on garrison or naval guns. Furthermore, the same forces acting on the wedge-shaped quoin used for applying elevation or depression often caused it to be violently ejected to the rear, to the discomfort of any hapless Gunner who happened to be in its way!
The same genius, to bolster his case, also claimed that trunnions with their axis aligned with the bottom of the bore formed a stronger union with the piece, a claim refuted by John Muller in the same treatise already mentioned. Muller's recommendation that trunnions be returned to their original position was ignored, one of the reasons which led him to remark, 'Our veneration for old customs is so great that whoever attempts to make any change is looked upon with contempt, let his reason be ever so plain and good'. Not until the middle of the 19th century was the Board of Ordnance finally convinced that the best place for trunnions was where the gunmakers of 1450 put them!
The elevating screw was invented in 1578, but not until 1760 was it adopted to any extent. Even then the Navy turned it down; they said it was too slow, and persisted with the quoin or wedge until the 19th century. To be fair, manufacture was difficult because the screw-cutting lathe had not been invented, and was not to appear for another 200 years.
Screws were usually designed to elevate the gun, say one degree, with a single turn, and were a great success in field artillery. Like the Navy Garrison Gunners retained the quoin until quite late in the 19th century.