I have owned several, different makes and calibers, from .22 LR to .45 Colt/.410. If you MUST have one, I'd recommend finding one of the old Davis small frame models in .22 Magnum. They are TINY, and can be easily carried in a shirt pocke, which , IMO, is the only reason to carry one.
The larger calibers are in larger and heavier guns, and for the weight and size you can do much better...a Charter Aems Undercover Lite is around 12 ounces empty, and no longer and not much wider than a larger caliber derringer. Gives you 5 shots of .38 Spl +P and a decent grip. Spend another few bucks and get a pocket holster or an ISP...
In the big calibers, I'd recommend the .38 Spl only. The .45 Colt is really large and heavy, and the round does not perform well at all from the short barrel...and the .410 from that same barrel is a joke. The quality large caliber derringers are very expensive, too...I had several American Derringer models, and could have bought a nice used snubbie revolver for what I paid for each of them...and I got very little back when I sold them.
They are neat to play with, but I would be uncomfortable carrying one, even as a BUG, and I have been shooting them off and on for fun for many years.
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