Ed- although Green Mountain uses 4140 for their ctg. brrels teels for BP rifles, they use something 'softer' or a different alloy for the muzzleloading barrels.

Round ball guns such as ours, with outside ignition fall into the 15,000psi range for max pressure & I 'assume' most RB barrels are made with this in mind. For CTG guns, the barerl companies usually use 4140, which is the standard for all modern rifles as well, but I don't know about the heat treatment, whether these BP ctg. barrels are acceptable to high pressure rounds. I shoot relatively low pressure smokeless in my .45/60 GM barrel regularly, expecting them to be in the 24,000PSI range or under. That big fat angled Sharps firing pin keeps my loads reasonable.

Shooting slugs greatly increases the pressure - witness the .45/70 - a mere 70gr. 2F, with a 405gr. bullet and closed ignition runs 22,000psi, a typical .50/90, about 24,000 and a .45 3-1/4 - around 30,000.

There was a question about wear. Naked, grooved lubricated bullets will wear the barrel less than any other form of patching. Steel would being the worse, then gilding metal, copper, paper,cloth, then naked being the least.