While I am here, IMA has a Purdey very similar to mine that has this description

"Research tell us that this very gun was sold to Jang Bahadur, then Prime Minister of Nepal, Unwin lists this Serial Number #4479 as being sold on the 31st of May 1850, officially listing it as A double pea rifle" costing 68 pounds five shillings. This type of rifle was popular for rooks and rabbits.
"
http://www.ima-usa.com/purdey-of-london-...-31st-1850.html

So, a 50 cal was used to shoot rabbits?