[Philip]

Originally Posted by fernando

On the Dardanelles cannon Michael Kritoboulus, a Greek dude that wrote the history of the Ottoman conquest of the Eastern Roman Empire under Sultan Mehmet II, describes the (some) foundry details of the cannon but kept silence on the technique used to cast the screw parts.
All we know is that its threads were sharp and clean as they were on the day they left the foundry and, according to naval officers who unscrewed the breech in 1868, it took a total power of 40 tons of jacks and man power to dismantle it.
Although we ignore what tools the Turks used for the operation, providing this ever took place, it is evident that the means used to unscrew it in 1868 were not properly a set of pipe wrenches. Also my theory on the gasses escape meets no case.

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Today's engineers and production managers can still marvel at this two-piece design connected by reasonably precise male and female threads, fabricated on a ponderous scale in a pre-mechanized age several centuries past.

I also wonder about the design of the apparatus built by the Ottomans to assemble these guns, and dismantle them as needed. The 1868 effort in Britain undoubtedly utilized the best resources of Victorian-era engineering and manufacturing, but that would be stacking the Industrial Revolution against medieval technology.

Pipe wrenches... yes, Nando, probably not however the underlying principles still involve leverage and rotational movement, generating enouth torque. The rows of circumferential lug-recesses, and very substantial ones at that in thick mouldings dedicated to the purpose, show us that Orban and his Turkish students had thought things out carefully. Barring the discovery of an illustrated Otto treatise on the manufacture, care, and feeding of these monsters, perhaps we can get an idea of what sort of mechanism was used from ancient texts dealing with mechanical subjects, by notables such as Archimedes, Vitruvius, et al. We do know that Islamic scholars of the Middle Ages were avid students of classical works on mathematics and the sciences.

Now, to your question of leakage of combustion gases from the joint. It would depend, I suppose, on how precise and tight those threads actually were. After all, in use the two components would be tightly screwed together much like the breechplug to the barrel of any muzzle loading pistol or shoulder gun. In other words, a "fixed breech". There shouldn't be any leaking of gases if the threading is suitably tight (ignoring for now the inevitable and small loss of pressure via the vent or touchhole).

Looking forward to other breech designs and how designers coped with gas leakage, it seems to me that this became a problem with breech-loading systems, which involved either a removable chamber-piece (the Portuguese berço cannon and its north European and Oriental equivalents being an example) , or a breechblock that pivoted, rotated, or slid in any number of directions depending on the system (Lorenzoni, Hall, Westley-Richards, Dreyse, Chassepot, ad infinitum) This is because with any movable-breech system, explosive gases will trump the best manufacturing tolerances.

Engineers kept trying different workarounds -- the Prussian Dreyse bolt action needle-fire gun (so named for its slender extended firing pin that pierced a paper cartridge to hit the primer) was a notorious gas leaker but its designers provided a chamfer to the barrel stub that fitted a rebated bolt face that directed most of the gas and particulate matter away from the shooter's face -- at least if there wasn't a headwind. The Frenchman Chassepot improved this greatly by designing his bolt action with an obdurator seal on the bolt head, made of a rubber like substance.. Worked like a charm but the gasket had to be replaced after so-many shots and a soldier's kit contained a special spanner and a packet of spares.
Early breech loading cannon with interrupted-screw hinged breech units would leak gas because the threads were interrupted to allow the opening of the breech and these channels negated the sealing action of screw threads (see above). Believe it or not, this principle was explored by several inventors way before the 19th cent. Discovery of rubber and like substances in the industrial age allowed the breeches to be fitted with obdurator seals analogous in function to the bolt gasket on the French needle-fire guns, and voilà , the result was quite functional.

The magic pill that cured gas leakage was the perfection of the metallic cartridge case, which contained projectile, propellant, and primer in a single, fixed unit. On firing, the explosion expanded the case enough to seal the breech effectively, and the inherent sturdiness of this "fixed ammunition" made for all sorts of possibilities in the way of repeating-fire arms, and ultimately those capable of fully-automatic rapid fire.