The blacksmiths of Italy and Spain that made the early gunbarrels usually used iron from old horse-shoe nails. There was no specific reason to prefer iron from horse-shoe nails, merely that a majority of the early barrel-makers just happened to be the same blacksmiths that dealt with making horse shoes and fitting them. In modern times, a person specializing in making and fitting horses shoes is called a farrier, but in the middle ages, the job of the farrier and the blacksmith were practically synonymous and the terms were used interchangeably.
The method used in Spain was to weld a bunch of nails into a strip of iron and then bend this into a cylinder about 5-6 inches in length. The strip is curled around itself twice so that the walls are double throughout the cylinder, for extra strength. To form a barrel of a certain length, multiple cylinders are selected and arranged end to end and welded together to form the barrel. The advantages of this method are that the metal is forged in smaller sections, so it is better wrought and purified. Also, if one of the cylinders has cracks or weld defects during its forging process, it can simply be discarded and another one substituted in place, when joining all the cylinders together to make a new barrel.
When this method was used, there were a lot of metal loss during the forging process. About 20 kg. of nails were used to make a barrel that weighed just 2.5-3 kg., but the resulting barrel was light and strong. Martinez del Espinar, the personal gun-bearer of King Philip IV of Spain, mentions that a quality gun barrel 1 metre long that is forged with this method should weigh just 2 kg. Making these barrels was labor intensive and expensive and hence this technique was used to manufacture barrels for the finest sporting guns of that period.
Another method of barrel manufacturing also became popular in France in the late 1700s. Barrels produced by this method were called Canon a Ruban or "Ribbon barrel". The method of manufacture, as stated by Marolles is as follows:
First, the smith starts off with a sheet of iron that is much thinner than the required barrel. This sheet is rolled into a thin tube that is the length of the barrel and slightly smaller than the required barrel diameter. This tube is called a chemise. Then a thicker strip of iron about an inch broad and chamfered to a point on either edge is heated a few inches at a time and wound around the chemise. This strip is called a ruban (i.e.) a "ribbon". To roll it around the chemise, they use a pair of tongs where one beak is short and flat and the other is rounded and long. The long beak is used to turn and press the strip on to the chemise. Five feet of ruban is used to make one foot of barrel. Since it is hard to make a barrel from a single ruban, the smith often made three of these separately, each one foot long, and then welded them together into a single three-foot long barrel. Then the whole barrel is placed in the furnace to heat it and forge it as a single barrel. Then the barrel is sent to the boring shop, where the chemise (the lining) is mostly removed using a boring bit, leaving behind the ruban forming the barrel.
This method produced a barrel of superior strength, as the welds were transverse to the barrel and could better resist the force of explosion. An example of a double barrel muzzle-loading weapon produced with this method is shown below:
(click image to enlarge)
Note that a part of the "CANON A RUBAN" inscription is visible, engraved between the two barrels, showing that these barrels was made using the above method. Also note the striping on the barrel showing the grain of the ribbon twisted around the chemise. The barrels have a beautiful appearance with figured patterns and have also been browned to protect them from rusting. The process of "browning" will be described later.
Another method that became popular in the early 1800s in Birmingham, was to roll a thick barrel out of a short strip of iron wound round a mandrel. The mandrel was then removed and this barrel would be passed between rollers with tapered grooves to lengthen the barrel, the edges being welded as the barrel passed through the rolls. This method of manufacture was severely opposed by the welding workers associations, as they saw it as a threat to their livelihood. Even though there were several riots, this method was used by several manufacturers because of its suitability for mass production of musket barrels. Muskets made using this method were often low-quality and many were exported to Africa as part of the slave-trade.