Beautiful workmanship! I can't imagine firing a .44 cal with an inch and a half barrel using today's high energy powders. Would be akin to a hand cannon. Even firing loaded with period powder, the short barreled Derringer is likely to capture the attention of the shooter and his prey pretty quickly.
The key to understanding a Derringer (sic) is the spelling of his name. The inventor spelled his name with one "R."
Others made pistols like the "Peanut" (one used to assassinate President Lincoln) and ones larger used two "R's" to get by infringement of the rights of the original inventor.
I got one of the reproduction kit guns by CVA of the Phila Derringer that was one of the first BP guns I ever acquired as a kid back in the 70's... I had to get my older brother to actually make the purchase since I was too young to do so at the time... it is 45 caliber.... a little hand cannon indeed... since its so light and small one habitually doesn't grasp it firm enough for the expectant hefty recoil that it does have... one of the most fun guns I still have to fire on occasion once in awhile... it will get your attention quickly....lol...