砲口初速
Early gun barrels were short and thick, typically no more than 26 calibers, as the gunpowder propellant they used burned very quickly and violently, and hence its acceleration time was short. Slower-burning "brown powder" formulations of gunpowder allowed gun barrel length to increase slightly in the 1880s but enormous quantities of brown powder were required. New slower-burning "smokeless powder" propellants available from the 1880s onwards such as Poudre B, cordite and nitrocellulose allowed a gentler prolonged acceleration, hence gun barrels were made progressively longer and thinner. The new formulations were far more powerful propellants than gunpowder and far less was needed by weight as they transformed almost entirely to gasses when burned. Muzzle velocity became limited only by the length of barrel that was feasible, both in terms of the construction methods of the day and in terms of any practical constraints imposed by the gun's manner of use.