In my opinion for the most part, pressure is not so much the problem. If ductile steel is used and pressure goes to high the thing bursts, which can be tragic if the shooter's hand is right there. Using steel with very low ductility across the grain, the barrel shatters which is considerably more damaging to the shooter.
Just for fun, I included pressure information in my 1985 Muzzle Blasts series. Tedious to copy from my pdf, but -
Oct 1985 pp 4,5 . . . published by John Bivins in 1982 . . . 80 gr GOEX FFg . . . maxi-ball can develop 21,500 psi. . . black powder rifle pressures may easily be in the 21,000 to 24,000 psi range. That is two to three times the working pressure of a modern 12 ga shotgun, loaded with smokeless. . . recent published work . . .Carl Wood, who showed that a 1/4" air gap could double the breech pressure in a .40 caliber . . . 50 gr FFFg resulted in 43,150 psi at the breech . . . comparable to normal smokeless pressures in a modern .44 Magnum revolver or .30-30 rifle.
I should read this thing again myself. I did write it as an engineer, so I suppose it is overly tedious for most people. As I review it I am even more impressed for the need of a bit of ductility in a barrel steel. I used to have an 1888 reference which I think indicated that British gunmakers knew this. Been a few decades, might be hard to find.
As usual, if anyone is willing to wrestle through this 1985 thing, send me your real email & I'll return a pdf, hopefully.