Thanks for resurrecting this thread Raimey. This has information about Whitworth, Siemens, and the stronger steels available c. 1890
https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit

Sir Joseph claimed in 1873 that his No. 1 Red Gun Barrel Steel had a tensile strength of 40 tons/89,600 psi, but other sources reported 66,000 - 67,200 psi; about the same as cold rolled decarbonized steel.