[boris]

"Maybe the energy he put into the cannonball by beating on it with a hammer has something to do with it as well."

Not a chance. Lord Kelvin would like a word with you.

--Boris

[zoso82t]

I know he wouldn't be putting much in, but assuming he is using a chisel, the friction of the chisel penetrating would create some heat, which could ignite the gunpowder.