He Gill
I think 5000psi is way low the powder wont burn as designed and the wad is not sealing. If the barrel wont handle 7000psi it wont handle 5000psi and it is over the hill. In a un neglected Damascus gun the barrels are as strong as steel tubes or stronger.
Remember recoil is a function of velocity NOT pressure.
I think steel barrels were much cheaper to make and the bad news about Damascus was marketing not fact.----- Cliff

wear those safety glasses