[Dead Corpse]

Was private ownership of cannons permitted by the founders?

Yes. The letter of Marque and Reprisal against the Barbary Pirates was to authorize the Federal Government to PAY privateers, share in the spoils, and to allow them to "hunt" pirates legally. Those letters quite clearly did not, as some here have suggested, make it legal for them to arm their ships in the first place. In fact, the reason the FedGov hired so many privateers was BECAUSE they were already armed.

[Free Trapper]

Private enterprises,like the early Santa Fe traders,sometimes took cannon along,also.

No "Letter of Marque" needed.