Pinyone,
Asking anyone familiar with British gunmakers if they ever heard of Nock is like asking folks on this board if they ever heard of Beck. The Nocks were a VERY famous family of innovative British gunmakers. I suspect that your piece was made by Samuel Nock (although other Nocks were at work in the 19th century as well). Samuel was a nephew of the more famous Henry Nock. Henry was famous for his pistols, fowlers, his patent breech, his volley gun, and his screwless Flintlock. He was a great inventor.
dave