(TFT) Cannon

["Jay Carlisle" <Jay_Carlisle@charter.net>]

Cannon and Economics

Data dredged up from various sources and far from complete.
1.75 inch bore - 3 foot long - 150 pound weight - half pound shot

4.75 inch bore - 10 foot long - 1500 pound weight - 12 pound shot

6 inch bore - 12 foot long - 3000 pound weight - 24 to 26 pound shot

7 inch bore - 10 foot long - 6500 pound weight - 42 pound shot - 1.5 mile 
range

8 inch bore - 8 foot long - 8000 pound weight - 63 pound shot

75 pound shot at a quarter mile range

Cast cannon main features.
Cascable or button
Breech
Bore
Base ring and ogee (ogee; a concave indention running adjacent to 
reinforcing rings)
Vent field (touch hole)
Vent field astragal and fillet (astragal; a convex = to > inch circle, 
fillet; concave junction)
First reinforce
First reinforce ring
Second reinforce
Trunnions
Second reinforce ring and ogee
Patch for foresight
Muzzle astragal and fillets
Swell of muzzle
Muzzle mouldings

As a rule of thumb a guns bore is about a third of the total diameter at the 
breech to about half the total diameter just before the muzzle swell.

Features like the button, ogees, astragals, and fillets were often decorated 
but also allowed for rigging and moving the pieces with block and tackle.

Various forms of copper, bronze, and brass were used in cast form through 
the early eighteenth century while lombards were made from strips of iron 
(strakes) held together by iron bands every 4 to 6 inches along its length.

Cast iron guns began appearing in the late sixteenth century but were 
subject to catastrophic failure causing shattering of the barrel into 
shrapnel instead of splitting (especially around the breach) like a Lombard.
Owing to this (as well as significant access to copper and tin) in 1599 a 
royal order in Spain decreed that all gallons carry only bronze cannon and 
all merchantmen had to carry at least 2 bronze pieces.
By 1725 cast iron cannon were the standard.

Casting is generally simpler and quicker than forging and iron is cheaper 
than other gun-metals, and casting methods tend to lead to some 
standardization.

The early guns we're talking about are smooth bore, black powder weapons.
There was a notion with these pieces that range was proportionate to the 
length of the barrel.
This is true for modern artillery, and small arms of the period, but not 
possible for these early guns.
The decomposition reaction in black powder has a burning rate that is 
essentially independent of temperature and, above a quickly reached 
threshold of about 350 psi., of pressure, or in the neighborhood of around 
64 ST for black powder pressure.
When black powder explodes, it increases in volume about 4000 times at 
normal pressure, so the effect is to produce a highly compressed gas behind 
the cannonball in a very short time. The products are 40% gaseous, and 60% 
solid. The solid fraction is expelled as a dense white smoke, which gives 
away the position of a battery as soon as it is fired. The combustion of 
gunpowder does not depend on atmospheric oxygen, because the oxidiser, 
saltpetre, is part of it.
Ergo propellant gasses in a black powder weapon expand at a relatively 
constant rate.
Experiment showed that for a twelve-pound field gun an absolute velocity 
threshold was reached at a barrel length of about 25 calibers (25 times the 
bore diameter). Data indicated, moreover, that extending the barrel length 
beyond 16 calibers resulted in a gain in muzzle velocity of only about 5= 
per cent while extending it beyond 12 calibers yielded only about a 12 per 
cent gain. Due to the effects of aerodynamic drag, which increases as a 
function of the velocity squared, these increases in muzzle velocity would 
have resulted in even smaller increases in range.
Additional factors such as the coarser grain of black powder, the larger 
charges, and greater windage (the difference between the size of bore and 
ball) also show that muzzle velocities of sixteenth-century cannon were not 
a direct function of barrel length.
Nevertheless many sixteenth-century cannon (including all of the culverins 
except perhaps Venetian ones) had barrels considerably longer than the 
length which would have produced the greatest muzzle velocity but this was 
for added strength and safety rather than for ballistic purposes.
Design proceeded almost completely empirically.
For example, French gun makers cast a 58 caliber gun for Charles V that was 
found to have poor range so it was progressively cut down to 43 calibers, 
gaining a significant range increase in the process.
Another test recounts a 36 pound gun 16 calibers in length (about 8.5 feet 
long) that was loaded with a powder charge one and one-sixth times the 
weight of the round dropping in muzzle velocity from about 1300 fps with a 
charge equal to projectile weight to about 1100 fps.
Even today black powder chemistry and gunmetal metallurgy are not fully 
understood.
Modern theory suggests that on the whole, sixteenth century cannon had a 
thickness roughly 50% greater than needed for strength.
Founders of the time however were not working with any well-articulated 
theory.
The stresses exerted by the powder charge are largest in exactly the 
sections of guns that were cast thickest.
The sixteenth-century cannon founder felt that he was best off using a melt 
of 80 per cent copper and 20 per cent tin, ignoring the 3 to 5 per cent of 
impurities of which he was generally aware, but about which he could do 
little. We have no theoretical basis for believing that he was wrong.
European guns were cast muzzle up (with a clay core to make the bore, the 
Turks put the muzzle down), and tin tends to migrate and cool last in a 
bronze mix typically leaving muzzles more brittle, ergo thicker.
The rule of thumb for powder charges in the 16th century was a powder weight 
equal to projectile weight.
That right there says I'm looking for effective range rather than a maximum 
for shots involving gunning Talent.
Also worth mentioning, 12 pounders and smaller tended to target crew and 
equipment with heaver guns firing at structure.

Ship construction (or building in general) is going to have a lot to do with 
all of this, but I'd be curious about any thoughts on cannon from the peanut 
gallery.

The actual acquisition of the materials required to produce guns and powder 
are separate technological and economic issues.
See the kings right to stable earth in England or France, or the island of 
Nauru (just over 8 sq. miles in area and largely blocked from guano export 
until 1907 because of German claims in the south Pacific), or Chile's 
Pacific war that landlocked Boliva, or the u.s. guano act of the 1850's, or 
etc., etc., etc.
Too much of a resource likely leads to economic Dutch disease.
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