But I'm not sure about carburization explanation. Wrought iron on the surface of barrel takes up carbon and becomes more brittle? What makes modern rifles more resistant to that? Maybe simple mechanical explanation would suffice - simple wear and tear?
Modern barrels are steel, not iron.
Yes. And in furnace steel can take up some additional carbon and turn into pig-iron. What makes wrought iron different when we talk about barrel material? Porosity because of remaining slag or is it softer or some other reason? I don't understand, what property of steel blocks the same process?
Cast iron with is very high carbon content was the result of iron ore smelted with coal or charcoal. REMOVING the excess required its being melted in another furnace where it was not exposed to the gases and the carbon was burnt off far enough to make wrought iron. This was then cast into "pigs" as well.
Cast steel of the early 19th c was also made in this way but it had a higher carbon content than iron but far less than cast iron. Today steel with less than 10 points of carbon is considered iron more than 10 points is steel.
Modern steel making does not have the techological problems much of it is made using electricity so there is no carbon added by the fuel. I will say this, steel unless carefully alloyed and controlled is not a really good barrel material. I think the weight of barrels in barrels from about the second quarter of the 19th c onward was the result of three things.
1. Much better powder.
2. The use of steel as a barrel material.
3. The possible use of Picket bullets from circa 1830 onward.
Poorly alloyed and inspected steel (this would be ALL of it prior to modern times and especially before about 1860-70) makes poor gun barrels. I suspect that this is why "best iron" was used in Rifle Musket barrels rather than steel.
Steel is stronger but can also be more brittle and some alloys have poor resistance to internal pressure. Since the alloy was largely unknown. About the only thing they controlled was the carbon content, to some extent.
Iron, as used in barrels of the 18th and 19th c is very ductile and even when riddled with flaws stands up fairly well it would seem. But back in the day barrel failures were common. Either due to poor welds or bad iron.
One of the reasons that Damascus was superior was that with the forging and welding and in the case of barrels made from horse shoe nail stubs, it well refined and much of the slag etc was burnt or beaten out of it. If welded properly the barrel was better than a common iron barrel. This is why fake damascus barrel finishes were common on cheap shotguns.
By the late 19th c there was machine made Damascus that was fully equal to Whitworth steel.
Still some barrels failed. In steel or Damascus barrels this is generally a brittle type fracture. Again unknown alloys. Still the pressures are so low and steel so strong that it should be impossible for a barrel to fail but they did. So it has to be workmanship or material related.
Improper loading should not do more than bulge a sound barrel made of proper materials and ML pressures. Even bulleted guns such as used in LR shooting with high pressure loadings (relative to RB or shotgun loads, only ring barrels when the bullet slides away from the powder. Or so I have been told and read. However, the bulleted MLs most often used for this are Italian copies of the Gibbs and these have modern barrel steel alloy barrels.
Why do steel barrels last longer? They are harder and more wear resistant. The material is not changed so much by contact with the hot, carbon rich gases and today we have much better rust preventatives than in the 18th and 19th c. Also the powder is much better and less is far less hygroscopic than powders made with saltpeter of questionably quality.
Then we have the frontier situation where until well into the 19th c even in some areas of the east firing a gun could bring someone around to KILL YOU. This was true in the west for far longer. So it was not a good idea to shoot then carefully wash out the barrel with water. Then dry the barrel carefully, then reload. Better wipe it a little with tallow and reload it. A pristine bore is of little use to a dead man.
So today with more wear resistant barrel material, better powder, better cleaning, barrels with lands and grooves that clean easier and better rust preventatives...... Barrels last longer.
For example: I can't see these barrels being easy to clean.
The second is from from a US "Common Rifle" the first from a Leman marked "Connestoga Rifle Works".
Dan