For the lead bullets used in many handheld guns/rifles, I can grasp the idea that the lead readily deforms to get a good grip on the barrel’s rifling, allowing for the transmission of torque to the bullet as it accelerates down the barrel.
But what about jacketed bullets, which may be covered with copper or steel? Doesn’t the copper/steel damage the rifling?
And what about larger artillery, which isn’t just jacketed, but actually has a thick case made of…what? Is it covered with a layer of something soft to engage the rifling without damaging it?
Artillery shells use what are called “driving bands”, which are narrow-ish bands of soft metal slightly wider than the shell itself that get deformed into the rifling and cause the shell to spin.
The link has a picture of a fired shell, showing the deformation. Here is a shot of an unfired shell- note the smooth band.
So the vast majority of the shell stays the same, except for a narrow copper segment that intentionally deforms to engage the rifling and seal against gas leakage. This is unlike a small caliber bullet, where the entire jacket deforms.
Barrel steel is much harder than copper or even the mild steel used to jacket some bullets. The figure I’ve heard is that barrel wear is accelerated by around 10 percent when using US Govt surplus copper washed steel jacketed bullets over using copper jacketed bullets. No idea if this still holds true for Eastern Bloc steel jacketing. My guess is that propellant gas erosion is a much bigger cause of wear than whatever the jackets are made of.
As to artillery, look up the term “driving band.” Or get ninja’d, like I did. I wonder if base-bleed or rocket-assist shells notably affect barrel wear in lafge artillery guns?
For larger guns a common technique is a driving band. The generally aren’t using steel to engage the steel rifling.
Copper is significantly softer than the barrel material so it’s still not a bad choice although it’s harder than lead. When steel is used in small arms it tends to be lower hardness levels than the steel used in the barrel. It’s will cause more wear than lead or copper but it’s not as bad as if a higher hardness steel was used.
Modern tank main guns have tended to move back to smoothbore guns. Driving bands are still used but don’t engage rifling. Even before that change started to happen driving bands that slipped were used with some rounds so that they imparted far less spin
Aside from clever design of the projectile, barrel wear was checked from time to time and the number of rounds carefully recordedto keep track of the state the barrel was in. Some guns had an extraordinarily short life span - apparently the Italian Vittorio Veneto battleships had guns only rated to fire 110-130 effective full charges.
So, was this an afterthought? One of the German ‘big guns’ of WWI had shells that had to be fired in a certain order, because each shell would cause a certain amount of wear to the rifling. Then, once they had all been fired, the tube would have to be sent back to be rebored.
I once had the log books for the 9 inch guns installed on Robben island, Cape Town in WW2 and they tracked all firings, most of which were quarter or half charges for practice. The barrels were about 35 years old when the were installed so the logs actually predated the rest of the site.
For those guns the limit was approximately 150 full charge shots before they would have to be sent back to Britain to be rebored.