Because they are copies of the Third Model { except for caliber) derringer, they were cataloged as the 4Th Model Derringer, Made for Colt by Butler. As noted these are not really shooting pistols ( but some do shoot them). The only way they have any real value is New In The box, and also if they were cased in a special casing such as a Book. Non firing Model Fours were also made for decorative purposes only. The guns are made of a alloy { Zetax?), some of the early guns did not have steel barrel liners and after a few shots , no rifling. A little more information would be helpful, is it new, any thing special such as Mother of Pearl Grips ( not plastic), engraved or what ever?? They did make some special order 4Th Models. ( They made a total of 112,000 of these little suckers plus Butler made a few thousand more under their own name).