Why Were Cannons Bronze?

This Bronze 1857 "Napoleon" is a Steen reproduction. They didn't shine like this in field use!

This Bronze 1857 “Napoleon” is a Steen reproduction. They didn’t shine like this in field use!

Long after the Bronze Age was over for swords, knives and pole-weapon heads, the prehistoric alloy was still used for cannon. Why?

Because while iron and early, uneven-quality steel were fine for contact or melee weapons, they weren’t a sure thing for containing the violent deflagration of gunpowder that launches cannon projectiles towards one’s enemy. Bronze could be cast and machined with high consistency.

It turns out that this question has already been studied at length — and we’ll quote from a 2002 thesis by Chuck Meide at the College of William and Mary. (The whole thesis will be attached at the end of this post as a .pdf. It’s full of gems like this).

Writing at the end of the muzzle-loader era, British artillery officer Manley Dixon in 1858 summed up nicely the required material qualities necessary to create ordnance:

The material should be hard, so as not to yield too easily to the action of the ball when passing out of the bore; tenacious, so as to resist the explosive power of the Gunpowder and not to burst; and lastly, elastic, so that the particles of the material of which the Gun is composed should, after the vibration caused by the discharge, return to their original position (McConnell 1988: 15).

 Bronze and iron were the only two metals with these requisite qualities available to historic gunfounders, and bronze was long considered the superior metal for ordnance manufacture. Up until the third quarter of the sixteenth century, however, iron guns outnumbered bronze pieces, though the former were almost all wrought iron, of decidedly inferior quality. The most powerful guns had to be cast, not hand-wrought, and as cast iron guns were overly heavy or dangerously unreliable, bronze was the material of choice throughout the 16th century. Though Henry VIII’s Mary Rose (wrecked in 1545) displayed a marked diversity of bronze and iron ordnance (Guilmartin 1994: 148) by 1569 the decision was made to equip Queen Elizabeth’s navy entirely with cast bronze guns (Lavery 1987: 84).

The main disadvantage of bronze guns was their price, which was generally three to four times higher than iron guns (Cipolla 1965: 42). In 1570 England, iron ordnance cost £10 to £20 per ton while bronze cost £40 to £60. With improvements in iron casting techniques, the price of iron began to fall by the turn of the century, and the difference in cost began to steadily increase, so that by 1670 iron cost only £18 per ton, while bronze cost £150 for the same amount (Lavery 1987: 84). As the principle maritime powers continued to increase the size of their navies in the 17th century, this cost became prohibitively expensive. An example, to put this greater cost in perspective: the four small bronze cannons carried as cargo on the French ship La Belle (wrecked in Matagorda Bay, Texas in 1686) cost more to manufacture than did the entire vessel! (personal communication, John de Bry, 1996)

Not surprisingly, rulers in the first half of the 17th century began to mandate and subsidize experimentation in iron gunfounding, in order to improve the quality of iron ordnance. Other than expense, however, bronze guns were still superior to iron ones in almost every way. Bronze was stronger, withstood the shock of discharge better, and lasted longer at sea. Bronze also was easier to cast, could be re-cast, and could be easily embellished with decoration. Because of this last quality, along with their hefty price tag, bronze guns also served as status symbols, an aspect whose importance should not be overlooked in the 17th century, when capital ships represented not only the might but the prestige of the king.

Despite the fact that bronze is 20% heavier than iron, bronze guns were lighter than their counterparts because the stronger metal could be used to make thinner guns of the same caliber (Tucker 1989: 10). The dramatic weight differences between bronze and iron guns of the same caliber are illustrated in Table 1 (keeping in mind that a gun of the same size and metal could vary by as much as 2-3 hundredweight or 224-336 lbs) (Tucker 1989: 10). The reduced weight of bronze ordnance was particularly important for field artillery.

Gun Size Bronze Guns Iron Guns
Length Weight Length Weight
shot weight feet cwt lbs kg feet cwt lbs kg
42-pdr 10 66 7392 3356 75 8400 3814
32-pdr 91⁄2 54 6048 2746 91⁄2 57 6384 2898
24-pdr 10 46 5152 2339 91⁄2 49 5488 2492
18-pdr 91⁄2 40 4480 2034 91⁄2 42 4704 2136
12-pdr 91⁄2 31 3472 1576 91⁄2 36 4032 1831
9-pdr 9 28 3136 1424 9 30 3360 1525
6-pdr 9 19 2128 966 81⁄2 21 2352 1068

Table 1. Comparison of the weight of bronze and iron British naval guns, ca. 1742. Adapted from Gardiner1979: Table 8. Original source, undated table in British Admiralty records (ADM 106/3067). “cwt”=hundredweight, or 112 pounds.

One especially salient advantage was that bronze guns were less likely to break while firing, and when they did the barrel usually bulged or split open longitudinally at the breech rather than explode. When iron cannon burst they tended to shatter and fly to pieces, which caused much more catastrophic damage to nearby personnel (Tucker 1989: 10; Kennard 1986: 161; Guilmartin 1983: 563). Figure 7 illustrates the striking difference between two failed guns, one of bronze and the other of iron. Improved iron casting techniques and gun design, however, would help solve this problem, though the reinforced guns had thicker metal at the breech and reinforces, increasing their weight. While iron guns were never considered as safe as bronze pieces, by the 1630s both England and Sweden were exporting iron guns of reputable quality (Cipolla 1965: 43; Kennard 1986: 161).

bronze_vs_iron_cannon_failureFigure 7. Two guns, one bronze and one iron, that have catastrophically failed (burst). The upper gun is a bronze 6-pdr, cast by Richard Gilpin in 1756 (526 lbs/238.8 kg, 4’ 6”/1.372 m long). This English gun burst at St. Lucia in 1783, tearing open longitudinally at the first and second reinforces. Currently housed at the Museum of Artillery Rotunda, Woolwich, from McConnell 1988: Figure 15. The lower gun is all that is left of an iron cannon that exploded, with massive loss of life, while firing on English troops invading St. Augustine on 10 November 1702. Photograph by the author.

The sole disadvantage of bronze as a gunfounding material was its propensity to heat up quickly, which meant that when firing a great number of shots in continuous action it was prone to becoming soft and susceptible to sagging or other bore damage (McConnell 1988: 15). Due to the nature of 16th and early 17th century naval tactics, however, this defect was not readily apparent; by the time of the great broadside to broadside slugfests of the 18th century, ships had already exchanged their bronze guns for iron ones. It would not be until the sieges of the Peninsular campaigns of the early 19th century that this defect became widely known (Kennard 1986: 162; Fisher 1976: 279-280).

What caused bronze to finally lose its throne? First came some centuries of technological improvements, which had English and Swedish gun makers producing solid, safe iron naval guns by the time of the American Revolution.

Terrestrial artillery was another matter. Bronze first was replaced in large siege guns in the early 1800s, but the weight advantage kept bronze 6-pounders and mortars in the field for the British Army in the 1850s and 60s respectively, and the US didn’t give up the smoothbore 12-pounder bronze Napoleon until long after other armies had done so — until the 1880s, in fact.

The thesis covers all this and more (including what all the confusing traditional names for muzzle-loading bronze artillery, such as culverin and falconet, signify).

Meide2002_Bronze.pdf

 

19 thoughts on “Why Were Cannons Bronze?

  1. Cannoneer No. 4

    Bronze guns didn’t stay rifled as well as iron and wrought iron guns. 3.80-inch James Rifles were notorious for this. Also, too high a rate of fire melts the vent, causing friction primer failure and misfires.

  2. Bonifacio Echeverria

    A most interesting post. In one of those ironic twists of fate, by the late XIX century it was the bronze the cheap option thanks to an Austrian named Franz von Uchatius. While Prussia was extending the advantages of cheap steel breechloading artillery (field arty at least) he came up with a process to give bronze very similar characteristics to steel when it came to artillery use for a fraction of the cost of steel for those countries without a proper steel industry. At least two WWI major players, Austria-Hungary and Italy, started the party equipped with bronze-steel tubes in significant numbers, some even in front line capacities. Quickly outdated by cheap steel in the QF pieces of the early XX.

    There were pieces of the same Uchatius system in use up until the Spanish Civil War, albeit in secondary roles (but with occasional front line service up until late in the war).

    1. Hognose Post author

      I’ll have to check that out. I know that the Škoda Works built their reputation on steel guns when most Austrian guns were still bronze, but they also went all-in on heavy guns because there was no competitor in the A-H Empire — they were buying these from Krupp.

      1. Bonifacio Echeverria

        Unfortunately, I can’t be of much help there. Not because I’m away from my library (not forgetting that Sp rifle list, just that it will have to wait till I conclude my present err… “summer operations” near the coast), but because the few bits I have been scavenging around in the Internet about the subject seem to come all from M. Christian Otner’s The Austro-Hungarian Artillery 1867-1918: Technology, Organization and Tactics. A massive book so interesting, that you can’t find a copy for less than 95 euros… (107$ for those in countries where doctors ain’t free) and thus so way outside my purchasing envelope for books, that I’m afraid it will never reach it.

        Main problem seemed to be not lack of tech ability but Habsburg level bureaucratic hesitation and infighting about what should be purchased next. When it was pretty obvious there was going to be trouble, the Emperor himself had to bang the table and tell his boys to take a decision, any decision, about field guns before dinner. It must have been embarrasing for him to be all bronze in the 1910s while everybody else, even the puny Serbs, had steel QFs. And they certainly had showed they knew how to use them in the Balkan Wars.

        Funny part, the steel-bronze guns were not overtly inferior per se in range or weight of shot. It was their lack of recoil management devices to allow them QF that made them obsolete. So, bronze was still mechanically viable as barrel material. Don’t know if by 1914 steel prices had not made it economically unsound.

        Probably it was. So I’m not surprised those enterprising Czechs at Skoda decided to try steel, but, IIRC, the main (only?) gun foundries in A-H were in Bohemia since Prince Liechtenstein’s times. Czech against Czech in the market wars. Now, there is a story, I guess. One for better pens than mine.

        I have been following the Spanish side of the story for the Sp Army adopted Krupp breechloaders with Ustachius bronze-steel barrels in the 1880s. Those were in Cuba. Then they proceeded to develop a local family of siege howitzers with the same type of barrels, no recoil system besides a wooden wedge. Those soldiered on until 1938.

  3. Ken

    This post could directly lead to the 2nd most discussed topic on milsurp forums – the single heat treat low number Springfield (the most discussed topic is whether Sgt York used an ’03 or M1917)

    Great post as always!

  4. archy

    ***Why Were Cannons Bronze? ***

    So they could make Victoria Crosses out of them after they were captured and melted down?

    1. Sommerbiwak

      The bronze letters on the Reichstag building in Berlin are made from two captured french artillery pieces from the napoleonic wars.

      Recycling cannon bronze seems to have been common.

  5. staghounds

    Krupp’s repeated fruitless efforts to sell ordnance officers on his clearly superior steel guns make for entertaining reading.

  6. S

    Just by coincidence, I happened across an interesting relevant tidbit yesterday:

    “For example the problem with the iron ore in the British Isles is that it contains too much phosphorus which makes the steel brittle. The solution – circa 1800 – was to add chalk to the molten metal* which caused the phosphorous to mix with the slag and the slag could be easily removed in the steel making process. This steel, should it contain some residual chalk residue, is not an alloy steel because no alloys were intentionally added to the steel to change the properties. Only to make the refining easier.”

    (Plagiarised shamelessly from the second half of the first para, found here:
    http://www.kanabco.com/vms/eng_metalsl_hist/eng_metal_hist_02.html)

    There’s probably a PhD or two in this, tracking down ore sources for the various major powers and the strategic implications; such as the “Quaker guns” that “armed” revolutionary US warships. Amazing what you can do when you point to black painted logs on your gun-deck when facing down a wavering Captain! How about the Hungarian cannon builder that enabled the muslims (ptui) to finally breach Constantinople, with iron guns? But, as we all should know by now, it’s the man, not the machine.

    I’d love to see a Hognosian exegesis of the cutting out of the HMS Hermione, as an example of superlative skill and determination (and monstrous balls of cast iron, or was it bronze?), triumphing against stupendous odds (and no friendly casualties….this is probably the most spectacular SF victory ever). I believe it’s an American weakness, now, relying on technology, when that horse has long since bolted from your stable (and ours, here). Time to look to your roots, and be grateful for the lesser things in life, like survival. We over here share some of the roots, but never had any of the fruit….but nevertheless some of us still survive. Weird, eh?

  7. 10x25mm

    In the era of artesianal metallurgy (roughly pre XX Century), bronze castings had much higher – and far more consistent – fracture toughness than cast iron. Plane strain fracture toughness (“K sub 1 c”) is the energy required to drive a preexisting crack into a material. Gunmetal bronzes (today’s CDA Grade 907) in the artesianal era had K1c values in the vicinity of 50 – 75 ksi root inches. Cast irons of the same era (and today) have K1c values no higher than 15 ksi root inches. Modern cannon barrel steels have K1c values exceeding 100 ksi root inches.

    The problem here was that even increasing section thicknesses could not prevent the inevitable rupture of cast iron cannon tubes, Increased cast iron section thicknesses only postponed the eventual rupture of cast iron cannon tubes. Sharp flaws (exceeding the ‘critical flaw size’, an inverse function of the K1c value) well below the limits of visual detection grew inexorable with every shot. Increasing section thickness did not increase the critical flaw size. A very few lucky artillerymen got flawless cast iron cannon tubes. Unlucky artillerymen died prematurely when their flawed cast iron cannon tubes ruptured.

    The low fracture toughness of cast iron also resulted in lots of small shrapnel projected in all directions when these cannon tubes exploded. The much larger critical flaw size in gunmetal bronze cannon tubes was easily detected visually and grew at a much slower rate under equal pressures. Fewer artillerymen were injured when a gunmetal bronze tube ruptured because its higher fracture toughness resulted in many fewer fragments. Smart artillerymen of that era inspected their bronze tubes frequently and lived into ripe old age.

    About the best that could be done with a cast iron tube was reinforcing the breech with a shrink fitted wrought iron ring as in the Parrott rifle design. Wrought iron had K1c values in the vicinity of 50 ksi root inches. Bronze ring breech reinforcement was also attempted, but failed due to its lower stiffness and greater coefficient of thermal expansion. The eventual solution was a cannon tube made entirely from Siemens-Martin process open hearth steel, which became generally available in the 1880’s.

    Decent technical discussion of the fracture toughness of castings here:

    http://www.intechopen.com/download/pdf/37419

    1. Hognose Post author

      In your third to the last paragraph, that seems to be what the thesis writer was grasping for in his illustration of the burst bronze cannon compared to the shattered iron one from St Augustine. (We have run another photo of this well-known display at Castillo de San Marcos before).

      Thanks for the detailed and informative comment!

  8. Slow Joe Crow

    Since it also involves containing explosions, where does internal combustion engine technology intersect with gun making? Nodular Iron, introduced in the 40s has a regular grain structure and high ductility which makes excellent engine blocks. Would it also make a good cannon? Is there any research into making a cast iron cannon out of better material? Also, in answer to S, Mauser rifles definitely show national variations in iron ore. Yugoslavian Mausers have thicker receiver walls than German or Swedish rifles because Yugoslavian iron ore had less tungsten so it was not as strong as Scandinavian steel.
    As an aside high performance motorcycle engines from the 20s to the early 50s frequently used bronze cylinder heads, or aluminum finning cast over a bronze inner structure for better thermal control compared to cast iron, or aluminum, until WWII aircraft engine technology trickled down and heads could be all aluminum.

    1. 10x25mm

      Gunpowder fueled engines were the very first internal combustion engine technology, with development commencing in the XVII Century:

      https://en.wikipedia.org/wiki/Gunpowder_engine

      Reliable ignition, fuel metering, and the fracture toughness of containment components were insurmountable problems in this era. Liquid fuels solved these problems and became the focus of IC engine development in the late XIX Century as mineral oil refining developed.

      Nodular graphite cast iron is far superior to the grey (flake graphite) cast iron used in the muzzleloading cannon tubes of the XIX Century, offering K1c values approaching 50 Ksi root inches. But the devil here is in the details, specifically the innoculation step which converts flake graphite to spherical graphite by changing the surface tension of the molten iron with magnesium or cerium. Successful innoculation occurs on a very rigid time line (it fades) and requires sophisticated laboratory confirmation. It is also a spectacular pyrotechnic display when uncontained. Thus it is best made in highly organized, high volume automotive foundries. Very few foundries offering bespoke castings pour nodular or compacted graphite iron.

      The ready availability of 100 Ksi root inch fracture toughness steel forgings and tubular products today diminishes the urge to make muzzleloading cannon tubes from advanced cast irons (nodular and compacted graphite) with their finicky innoculation step. The only issue with steel muzzleloading cannon tubes is breech design, but mechanical threading (combined with welding if cosmetics are paramount) provide steel tubes superior to any cast iron tubes.

    2. archy

      ***Since it also involves containing explosions, where does internal combustion engine technology intersect with gun making? ***

      Not *just* internal combustion engine technology, but also that of the older external combustion [ie: steam engine] technology and that of the parallel railroad and steamship industries. Improved steel castings for everything from railcar wheels to higher-strength couplers allowed the advance of railcars capable of 50%-100% increases over their predecessors, which meaint that higher strength couplers had to be developed, allowing trains of double or triple previous lengths….once better brake shoes were also developed. In steamships: see in particular the details of the brittleness of the steel hull plating of the RMS Titanic in cold waters, which likely contributed to the fatal damage to the ship following the iceberg collision…and that being state-of-the-art for a 1912 ship, how many of those built just before or during the 1914-1918 Great War were all that much better?

  9. Keith

    Excellent post and responses here all. Please do more. I learned more about this subject just reading this than I ever had in the past.

    1. Hognose Post author

      Hey, Aesop, go big or go home:
      http://steencannons.com/fort-donelson-dover-tn/

      Currently we are making a 32-pounder Seacoast Gun

      The Napoleon is here:
      http://steencannons.com/cannons/u-s-model-1857-12-pounder-napoleon/

      Price: Aluminum Non-Firing – ($4000.00 | Cast in Gray Iron with full bore-($12000.00) | Cast in Gray Iron with sub-bore of 3.62 ($11000.00) | Cast in Naval Gun Bronze with steel liner-(Call for pricing)

      That’s not including the Nº2 Field Carriage (figure +$10k)
      “Call for Pricing” = “If you have to ask, you can’t afford it no matter how frequently you get in line with the meth addicts, heroin addicts and methadone addicts and sell your blood.”

      1. Aesop

        Ceud mile taing, your Hoginess.
        Steen website added to my Wish List folder.

        1) Those prices induce no sticker shock. Sounds like a reasonable amount for the bronze version.
        (Still a pity that no one cast them in ordnance steel, but I’ll get over that.)
        2) They’re still, somehow, street legal here in PRK.
        3) I’m going to be the first on my block, etc. etc.

        Item Two on the agenda will have to be an open account with a shot put manufacturer.
        I know cement-filled coffee cans are the current substitute, but I’m a traditionalist at heart:
        A cannon that pretty without a handy nearby stack of ready cannonballs would be like pancakes with no syrup.

  10. Light Dragoon

    One of the problems with Bronze guns too was that they wore quickly with the cast iron cannon balls in common usage throughout their period of use. Interestingly, at least as of 1846, the Mexican Army was using copper cannon balls, which being somewhat denser than iron also gave the Mexican artillery slightly better range than the US artillery facing them (at least at Palo Alto Battlefield, where several Mexican copper cannon balls have been recovered.) Not that it helped them much, since the American “Flying Artillery” would gallop up to 40-50 yards in front of the Mexican infantry formations and let loose with canister.

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