It sounds like a fencing musket. they were made by a number of makers in England from the 19th century.
Joe Salter has a Webley & Scott for sale now:
http://www.joesalter.com/detail.php?f_qryitem=12880
This page has a bit of info on the muskets and images of a Greener example:
http://www.rifleman.org.uk/Fencing_musket.htm
Hope this helps
J