 Another method of increasing firepower was to vary the projectile fired or the nature of the propellant . Early ironclads used black powder , which expanded rapidly after combustion ; this meant cannons had relatively short barrels , to prevent the barrel itself slowing the shell . The sharpness of the black powder explosion also meant that guns were subjected to extreme stress . One important step was to press the powder into pellets , allowing a slower , more controlled explosion and a longer barrel . A further step forward was the introduction of chemically different brown powder which combusted more slowly again . It also put less stress on the insides of the barrel , allowing guns to last longer and to be manufactured to tighter tolerances . 
