What kind of medieval armour and weapons can you make using today's sciences?

[Aeson]

@Aeson cannister refers to the rounds being in a cannister of some sort to keep them grouped together in flight, the rounds are over an inch in width. The rounds got smaller in the mid-Ninteenth century as the cannister got more solid instead of wood and ropes, but they are not small rounds. Grape is literally just packed rounds fired at close range from the cannon, the size is in the name.

'Grape' refers to the shape of the munition - it looks like a bunch of grapes - not to the size of the shot.

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Also, I invite you to peruse the Ordnance Manual for the use of Officers of the United States Army, 1862 edition, if you disbelieve me that the balls used in canister are smaller than the balls used for grape.