Greg Bond built one of his 1st derringers for my wife, .357 mag, and truth, it is decently regulated, both barrels will hit an orange at 10yrds, with the same sight picture, and in real magnums, is not bad, the .22rf or .22mag, more ammo yes, tree rat or rabbit at 50" or more, I have not shot one, but doubt the design would allow it, as to the .45/410, I do think it is viable, with birdshot, for short shots at snakes and such, .45 colt, bigger critters, with the Eley 3 or 4 pellet SD, definitely. Beyond 15 yrds on anything smaller than say a 15 lb animal, not so much. Putting together a small survival kit that included it, yeah, I can see that, of course you can have shot capsules in .38 and .357 too. Ream it out to .357 maximum, and now you have a real fire starter.