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Originally Posted by Jim McDougall
I am intrigued by some of the elements of the firing of such cannon, and hope I might pose some questions regarding things brought up here.
The flash and sparks would come out the end of the barrel, but how much heat would be released from the touch end of it as it seems the explosion would be contained?
There seems to be a great deal of attention to the quality of powder, and I recall in study on the Seige at the Alamo, one of the pressing issues was the poor quality of the Mexican black powder that had been captured
I recall reading on the Alamo battle that the Mexicans with their poor powder had to load extra to gain sufficient charge, thus they had to hold their muskets at the hip to avoid the pan flash which would burn their faces.
If I understand correctly, the powder used in cannon is different than that used in firearms.
Could the same have been the result in firing, and damaging, of Mons Meg?
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Having stood near a fair number of muzzle-loading cannon when fired, I can say that most of the combustion byproducts would emerge from the muzzle end. The touchhole is typically 1/4 inch in diameter or a bit less, there will be some spark and smoke spurting upwards out of it but not enough to pose a real risk in and of itself. The thing to remember about these guns is that there is no recoil-absorbing mechanism so the entire cannon rolls back on its carriage if fired with a full load + shot. That is why artillery drill called for the crew to stand back and to the side at moment of firing. The cannoneer, in particular, had to be completely clear of the wheel(s) or the carriage trail when he applied the linstock, or jerked the fulminate primer cord. The recoil of a large gun could crush a man to death. Also, standing back was especially beneficial to all, in order to avoid inhaling a snoutful of sulphurous smoke, made worse if the wind was contrary.
Re the quality of gunpowder. It depends not only on the formulation and care taken in manufacture, but the conditions of storage and transport. Black powder is notoriously unstable. It is hygroscopic (moisture-absorbent; consider that carbon and saltpeter are primary constituents) and thus has a limited storage life (compared to modern nitrocellulose powders) unless kept well sealed in very dry conditions. Jim, have you found out anything about the manufacture of powder in Mexico during the period in question, or the level of the country's military supply and logistics?
If Mexico was anything like the late Qing Dynasty, corruption had its effect on military provisioning. A common trick played by contractors supplying gunpowder during the Opium Wars period was to adulterate it with sand. So much so that it sometimes failed to explode. The cannon-founders realized this so they took shortcuts in the casting process, and used inferior alloys. The result being that most 19th cent. Chinese cannon, with the exception of those made in French-supervised plants in southern China, were not much more dependable than the wrought iron bombards of late medieval Europe. The ruling Manchus were apparently too fixated on their heritage of shooting arrows from galloping horses to take the problem seriously enough.
So why did Mons Meg burst in 1680? Not having seen a metallurgist's report, I can surmise that it was likely due to structural deterioration of the forged iron components over two centuries, and moreover that it was probably loaded with the more powerful corned or granular powder as opposed to the early, weaker meal powder with its slow and inconsistent combustion rate (see my first post explaining this in some detail). The evolution of barrel construction tended to go lockstep with progress in propellants. This is why today's shooters of black-powder weapons, including replicas made to modern metallurgical standards, are warned never to load with nitrocellulose powder.. Even the breech loading double barrel shotguns, made of damascus steel, from the late 19th cent must always be used with black powder shotshells.