If the gun store doesn't deal with antiques on a regular basis or know you well, I wouldn't bother with it. They'll just try to look it up in the Blue Book of Gun Values & tell you what it says. You could do the same if your library has a copy.
See what this guy can tell you:
http://www.armchairgunshow.com/index.htm
I've never dealt with him but I do check the web site a couple times a year & there are always antiques listed for sale.