Gun Casting

A nice representation of 17th-century gun types with a culverin, cannon, perrier and two types of mortar and showing the different proportions of each weapon.

Since muzzle-loading smooth bore guns were the most commonly encountered form of artillery used during the war, it would not be out of place to describe the casting process that produced them. Bronze and iron gun casting processes were very similar and both started with the manufacture of a model. The model of the gun was made of wood built up with clay. The clay was built up on a wooden spindle, which was sometimes a reused ship's spar. This was greased and then wound with rope. It was then suspended between two trestles and continually turned while a mixture of loam and horsehair was added to the rope surface to build up a model of the gun. Once the clay model had reached the right




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size it was shaped witli a strickle board to gain the desired shape. The strickle board was held against the side of the model, shaving off the clay as the model turned, until the right shape was achieved. Normally the model was extended at the muzzle end by about two feet to form the dead head. This is the part of the mould that would take the excess metal. It should be noted that the breech was not added until a later stage. Once the model was finished it was dried by heating and a thin layer of wax was applied to the surface to aid its later removal from the mould. Wooden models of the trunnions were then attached to the model, placed slightly nearer the muzzle than the breech. This gave preponderance to the breech and made controlling elevation easier. Finally, wax models of the decoration and dolphins were fitted. In most cases this was done by fixing a small mould to the model's surface and casting the item onto it. The moulds were then removed, leaving a wax model of the surface design. The whole model was now coated with more clay of a different type and diluted with water. Four or so coats of this clay were applied and then dried, and then larger quantities were applied to a thickness that depended on the type of gun: the larger the gun the thicker the mould. It is important to bear in mind that the gun barrel could weigh up to two tons and so the mould had to be able to withstand the weight of the molten metal. In order to guarantee this, the mould was bound with iron hoops to reinforce the clay.

Once the mould was bound, the model, or positive image of the gun barrel, had to be removed. This was done by removing the spindle with a mallet. As has been described, the spindle was covered with a rope wound around it that could be removed and the wooden patterns for the trunnions pushed into the mould and then removed. The rest of the clay

A typical 17th-century fortification with a bastion and outer wall. The gun is mounted to cover the lines of circumvallation that the besieging army has taken up.

Armies facing each other in the field. The guns are drawn forward of the main battle line where it is likely that the heavier ones would have been placed. From a French manual of 1635.

model now had no central support and began to collapse, leaving a negative impression on the mould itself. The mould was internally checked and any stubborn clay pieces were removed. In the end the mould would be a near-perfect negative replica of the gun. The breech mould was then attached at the end of the gun. This had to be made separately so that the spindle could be removed. In the I7th century all guns were cast using a central core. This was an iron spindle, which was covered in clay and horsehair. The core was eventually to form the bore of the gun. The final layer of clay was applied and a strickle board or shaper was used to replicate the calibre of the bore of the gun. If the gun was a perrier (a gun that fired stone projectiles), the bore needed to be shaped at the end and therefore the core was shaped to represent this. Chaplets, iron rings with four radiating arms, were used to secure the core at the top and bottom of the mould in the central position of the bore. It was critical to the use of the gun that the bore axis was parallel to the axis of the gun. If it was off-centre this rendered the gun useless although some defective guns were still used in spite of this. Sometimes chaplets were fixed into the breech mould but many were fixed into the bottom of the main mould. At the muzzle end a similar device held the core. It is still possible to see chaplets in existing bronze guns of the 17th century. If one looks at the surface near the breech end one may be able to detect a small, corroded iron slot. This is the end of one of the four arms: the chaplets, being sacrificial, were cast into the bronze body of the gun.

During casting, the moulds were placed upright in a pit and then earth was built up around them. Channels were created at ground level to let the molten metal from the furnace flow to the heads of the moulds.

From the same source as the previous photograph but this time the guns are placed behind a natural defensive feature and appear to be firing over the heads of the advancing cavalry-

The tapping of the furnace and the filling of the moulds were the culmination of the process and it was common for dignitaries to be invited to see the process. Once the moulds had cooled it remained to dig them out of the pit and actually break them open to get at the cast guns. The core of each still had to be removed and, because a clay lining surrounded this, it could be loosened and gradually removed. The gun was then subjected to a cleaning-up process that included cutting off the dead head. This large extension to the muzzle had to be sawn off by several men using a simple hand-held saw. The bore itself had to be bored out to ensure that it was true and that no burrs or projections would cause problems with firing. A vertical, horse-powered, boring machine normally carried this out. The amount of metal to be removed from the bore was only the windage or the gap calculated to be required between the shot and the wall of the barrel. This gap was normally about a quarter of an inch and if the gun was bronze this required relatively little power. The gun barrel was suspended inside a wooden tower by means of a pulley and the chase and breech were clamped into a movable frame. Beneath the muzzle of the gun was a cutting tool on an axle. The axle was rotated by a horse pushing a beam at right angles to the axle and the gun barrel was lowered onto the cutting head. Any flexing of the axle or misalignment of the tool could ruin the gun, so it was essential that the person conducting the operation was extremely careful.

Once the gun was bored and finished it needed to be proved. This normally consisted of firing it with a large charge of powder and perhaps a round shot. According to Nathaniel Nye in The Art of Gunnery:

From the same source as the previous photograph but this time the guns are placed behind a natural defensive feature and appear to be firing over the heads of the advancing cavalry-

All peeces that shoot a bullet under 10 pound weight and duly 8 fortified with metal, being shot 3 times, first with the whole weight of the iron bullet. Secondly with 5/4 parts thereof and lastly with 3/2 parts of the same will hold for any service, being charged with her ordinary charge, albeit the said peece were discharged 100 times per day.

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