"Iron vs Bronze for Gun Tubes" Topic

Iron is a 'lighter' metal than the bronze alloy. However, as it is brittle and tended to crack or burst during firing, much more had to be used to make a serviceable gun tube which could affect mobility in a field piece. That made iron guns of the same caliber heavier than the bronze equivalent gun tubes.

Iron was used for naval and fortress/garrison artillery as it wasn't moved. Bronze was used for large caliber siege guns, such as 16- and 24-pounders. This heavy artillery was usually moved after being disassembled and moved in specialized artillery vehicles such as sling carts and devil carriages. There were limbers for siege guns which sometimes only moved the gun carriages with the gun tubes dismounted and those were moved by the vehicles already mentioned.

Another reason for using iron for naval guns was the fact that sea water (and salt spray) does not play well with bronze.

Most naval guns were bronze until the 17th C. and there were still many bronze naval guns well into the 19th C. How did they keep them from turning into green flakes? I really don't have a clue.

Same way that they do now – gun oil and elbow grease.

Yes, its a curious balance. Iron is less dense than bronze and is actually stronger by some measures, but has a "brittleness" (perhaps a forum reader knows the correct metallurgical term) that could only be corrected at the time by adding thickness.

Anyway, the barrel of a so-called short iron 6-pounder in the AWI weighed a good 150 pounds / 10% more than the comparable bronze barrel, while the difference for a long 6-pounder was 475 pounds / 25%. On the other hand, the iron field guns were rated for a powder charge of up to 1/3rd the weight of the shot, versus 1/4 the for the bronze, so the heavier iron gun had longer range for roundshot and greater punch for canister and case.

Last but not least, although an iron barrel was cheaper to make, bronze barrels once worn out could be melted and recast; iron was just scrap. This, along with a lack of suitable ironworks, was key to colonists' preference for bronze.

What reference did you use for the weight of the 6-pounder?

The standard British light 6-pounder of the period weighed between 527 and 590 pounds, English measure (depending on what conversion is used for the British hundredweight).

The Russians decided to go for Krupp copies built of bronze in 1877 for many of the reasons noted her, plus they had the facilities to cast bronze guns and it was seen as cheaper.

Rawdon, brittleness IS the correct term.

…canister and case…

Canister and case shot were the same round.