Where is this museum? The UK? Not many Mantons made it to this side of the pond.
There were two Mantons, brothers (some sources say half-brothers), John and Joseph. John was employed as foreman in the shop of a man named Twigg, and then set out on his own. He became the leading gunmaker in England in the period roughly from 1810-1825. He was "By Appointment" and all that, gunmaker to the Prince of Wales and the Duke of York. He died in 1834.
His son, I think also named John, continued the business through mid-century, but was not considered as fine a gunmaker as his father.
Joseph Manton became "top gun" from about 1825 to about 1835. In 1816, he patented a percussion system using a pellet, and in 1818 one using a tube lock. He died in 1835 and his shop was taken over by a William Golding.
If you are in the UK, there are a couple of books on the Mantons and their times; they were pretty famous. Any large library should have them unless Tony banned gun books as well.
OK, now tell me about a lever action Winchester in .30-30 and .410. Sounds ... well, interesting.
P.S. I won't change the above, but I now see you are in Canada.
[This message has been edited by Jim Keenan (edited July 12, 1999).]