I know its an old gun but what kind and how old?

Well older then you..... maybe....

My guess its a very early model or at least a replica of a very early model. I would say check what Colt's first product was and all other American gun manufacturers. If that yields no results, then I would try European. I would date it between 1840-1860. The first cartridge was developed in 1838 so it would have to be sometime after that. I would not place it past 1860 or 1870 because at that point, pistols manufactuering was more streamlined. The corrugated barrel tells me that possibly, the metal working at the time was not as good as it was in later years.

~S~
Octogon barrels were heavy of course but were beleaved to be stronger,and they wuz.
earlier barrels that were round were wrapped barrels(onion Peel) and wuz weaker.

I took it to a gun shop, all he could tell me was it was european. I haven't had to time to go through all the old papers and pictures I have to see if I could figure out some history about it and its owner. thats a someday project.

I saw a picture of one just like it at the International European WWI Living History site I think. IIRC, was Russian, early WW-I: http://europeanww1lh.forumup.be

The "Just pistols" guys might recognize it: http://www.justpistols.co.uk

~S~
a friend of mine bought one simlar to this one and it was swiss made and shot a rim fire, I think a 12 mm , i might be mistaken looked like a 41 swiss cartradge.
I been looking but found nothing exactly like it.