I believe the soda can mortars refer to the the size of the opening and what it shots as opposed to lobbing lead shot spheres as the seem to be discussing here. At least the ones I have seen the idea was the bore was the size to hold a soda can. The other sized one is for tennis balls.
The idea behind soda cans and tennis balls was you,could remove the missile from the mortar or cannon if it should miss fire and not launch. As removing a hunk of lead the size of a tennis ball approximately,safely or with out danger to remover could be problematic. If it did go off, you might have no need for a fancy suit or a open fancy lined resting box. :o ;)
As for hitting the neighbors house, with a hunk of lead that size can you say. In trouble with the authorities up to and past your epaulets.