You have a very nice silver mounted Anderson Lamb rifle. He was born in 1815 and lived until 1891. He was the brother-in-law of William Lamb. Anderson was the most prolific of the 85 Jamestown School gunsmiths. I have owned dozens of his rifles and currently have two of them for sale. His gun shop was located on the north side of Mackay Road and on the west bank of Bull Run creek in Jamestown.
Your rifle looks to have survived in very good condition. The full silver side plate and all silver mountings indicates this was a high end rifle made in the early 1850's.
I have a book available on the Jamestown School if you are interested in learning more.
Michael Briggs