The Jaigarh Fort and its cannon ...

[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.

[fernando]

Filipe, what a treatise !!!
Definitely your luggage of these things scares me off discussion.
Still, the only experience i have in this particular, is an article (where i was most kindly appointed co-author) on the Westley-Richards (Monkey tail) pistols, of which i had a couple at the time; a version that ended up being only produced for a Portuguese contract (1000 units). Incidentally their failure to be accepted by the British Board of Ordnance was not a gas leakage issue, described the Board as "absolutely gas tight", but their non military advantage.
Back to early artillery, i dare realize that those Orban/Munir Ali guys were smart enough to circumvent problematic solutions like those applied to Berços, for one ( direct plug into barrel and quarter turn rotation), or any other pivoting systems. A screwing principle; not just a quarter or half turn method but, the whole of four threads rotation. This prevented their minds to predict the advent of the gasket or the washer. And adding to the fact, according to the Brits that, the threads were impeccable, i wander if even Lucifer could escape through them. This still not excluding some lubricating/sealing resource, like organic grease.


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[Philip]

Obrigado, Nando, pela reintrodução ao sistema retrocarga "rabo da macaque".

Quite an interesting system since it was apparently self-lubricating.

Back to the screw breeches of the Orban cannon -- you mentioned some organic grease as possibly having utility as a backup sealant if the threads were not fitted tightly enough. I'm thinking, in such eventuality, the natural tendency of black powder to form all that dense residue during combustion would have served the purpose quite well since it would have built up during successive shots without the breech being opened each time.

The observations made by the British, and the Greek expert you mentioned, about the quality of fit of these screw threads (as pertaining to the so-called Dardanelles gun) is still an amazing thing. Considering the era in which it was made and the nature of measuring tools and fabrication processes at the time.

And especially when you compare these achievements with the Portuguese introduction of their methods of gun making to Asia. The armory at Goa improved greatly on the basic processes in use at the time, and brought the concept of threaded breech plugs for musket barrels to the Orient. However, as historical literature and surviving guns show, Asian cultures did not take naturally to the turning of screw threads despite their skill in other aspects of metal craft.

It was a difficult lesson. In Iran, the Persian gunsmiths did not even trust the method (maybe to hide their lack of motivation to master the skill?) and through the 17th cent. preferred to use forged-in-place plugs (often anchored with a cross pin), saying it was stronger. The Japanese were almost allergic to screws, they used similar means to seal their barrels and even avoided all screws in constructing their gun locks, which were made all of brass to better suit the assembly methods they preferred (same for the Malays). A scholar writing a PhD thesis on the introduction of guns to Korea shared a Japanese text with me, describing the earliest attempts to cut threads in iron in that country -- the craftsmen tried to use chisels to shape the spiral, which was doable but far from ideal for male threads but virtually impossible for the female threads.

Indian and Chinese artisans eventually got somewhat comfortable with screw threading thanks to repeated experience with European technicians, but when it came to firearms, the tendency to avoid it was still apparent into the 19th cent. Very few Indian toredors or matchlock muskets use anything other than pins or rivets to secure their parts.

So we have to give those 15th cent. Turks A LOT OF CREDIT.