Elenco Bombard - Manual (Page 9)

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Leonardo also designed the breech-loading cannon, an improvement of muzzle-loading
cannons that required a fast means cooling before another firing. Da Vinci planned for
the use of several cannons in rotation so one could be fired and one loaded while the
third one cooled.
Da Vinci also measured the penetrating power of a missile, and varied it by changing
the attitude. During these tests he launched a rocket-powered cannonball that is
thought to have shot ten thousand feet into the air.
Da Vinci also made improvements to the steam cannon and in his new design, had
the breech of the canon built into a brazier of burning coals, heating it to very high
temperatures. Following this, a small amount of water would be added just behind
the iron ball. When the water turned to steam, it would drive the ball out under
pressure. In his handwritten notes, Leonardo quoted how large a cannonball this
weapon could fire, and how far it would travel. It is quite quite possible that the
inventor actually built and test-fired this cannon.
When it came to projectiles, Leonardo wanted to have more effective ones and designed
shells filled with gunpowder which exploded upon impact; others contained projectiles
which would scatter over the area. One design sees a large ball split into two pieces as
it leaves the mortar. This sends smaller balls in all directions and they, in turn, explode
upon contact.