I wonder if they were trying to make shaped charges or just placing omnidirectional explosives in strategic locations (or even artificially creating confinement). Brass was better (and more expensive) ...

First used for battle in China in about 900 A.D., gunpowder spread throughout Eurasia by the end of the 13th century, eventually revolutionizing warfare as a propellant in firearms and artillery.

I would love to see some of the 14th~15th century records they used - the contemporaries must have had internal records of 'research data' as well, if the product was to be used in mass-manufacturing ...