Connor, the BRNO sidelocks are VERY nice guns indeed.
Interesting note on shot sizes, kuduae. My friend;s gun was one of those old, twist steel barreled SxS's that came over by the barrel full. Loose action and all, but it never "let go".
He does not use it any more. This was back in the 90's, when he used to shoot ducks with it.
I have a couple .410 singles already. What might be interesting, is if it had thick enough barrel to rifle. I'm thinking of lead bullets and black powder.