Derringers (small two-shot handguns) almost invariably have hammer springs which are too stiff to allow for effective single-handed use. Since anyone who is unfortunate enough to need a derringer will likely have an attacker practically on top of her, it's unlikely she'd have both hands free to cock it. While some firearms may be safely carried while cocked (the classic Colt pistol design of 1911, for example) derringers don't have the trigger guard, thumb safety, or grip safety of the 1911 and may thus be decocked for carry.
My proposal would be to equip the derringer with three springs (all in the grip). One of the springs would work like the ordinary mainspring, but would be much weaker. That spring would be kept decocked except when the gun was ready for firing. The other two would be stronger and would be normally kept cocked. Pulling the trigger with all three springs cocked would release the hammer and the first 'extra' spring, which would add enough power to the hammer to make up for the weaker mainspring. After the first shot was fired, the hammer could be recocked easily (just cocking the mainspring; leaving the first 'extra' spring decocked) ; pulling the trigger again would release the hammer and the second 'extra' spring.
Mechanically a little tricky, but should nonetheless be feasible. The design of the gun would be such that when the hammer was down even unintended release of the other springs (e.g. if the gun was dropped) would not make it fire.
Sound at all plausible?-- supercat, Feb 21 2002 Electric ignition for all modern firearms. Problem solved.-- dsm, Feb 21 2002 Sounds too complicated. Do you really need additional springs? It sounds like you want to convert the hammer to do double duty as a safety. Maybe you could combine the functions like this: You cock the hammer, and then the spring is tight and the gun is ready to fire. If you lower the hammer at this point, the gun put on safety, but the spring stays tight. If you pull back the hammer a second time, it is easier, since the spring is already tight, and the gun is off safe and ready to fire again. If you lower the hammer, and then pull the trigger, it releases the spring but the hammer does nothing, so it does not fire. It should also have an internal safety that is removed only when the hammer is back and the trigger is pulled, to keep it drop safe. Double locks and barrels would probably be the easiest way to make this work for your second shot.-- Krate, Feb 21 2002 My prefered solution to overcome potential technical difficulties when attempting to murder someone is to keep it simple. Forget the derringer, and stick to a muckle great bit of wood with a rusty nail rammed through one end.-- mcscotland, Feb 21 2002 mcscotland: Someone who intends to murder someone isn't apt to use a firearm that's only useful at near-zero distances. They'd be far more likely to use something silent (like a knife), something that works at much greater distances (like a hunting rifle), or something that doesn't require them to be anywhere nearby at all (like a bomb). A derringer is really just about the worst-of-all-worlds as a murder weapon. On the other hand, except for cocking the hammer, a derringer requires much less strength to use effectively for self-defense than a knife, and if the loud bang summons assistance so much the better.
Krate: Derringers are already double-barrel firearms, but generally only have one hammer [a moving transfer-bar or firing-pin arrangement selects which barrel is fired]. You pretty well understand the concept of how I'd have the thing work, but with the caveats that [1] with the hammer down, the trigger would be disabled. A sufficient jolt might cause one or both of the booster-springs to decock, but the trigger would not; otherwise normal handling would almost certainly bump the trigger since there is no trigger guard. [2] Opening the action would be necessary to recock the booster springs (after the first shot is fired, cocking the hammer should not try to cock the first booster spring since that would make it very hard to get off a second shot). I would probably have the gun cock one of the booster springs on opening; the other on closing.
As for the internal safety to make the gun drop-safe, that would be a given. Simply arrange so the barrel-selector is in a neutral state until the hammer is cocked for use.-- supercat, Feb 21 2002 personally supercat, I would hold the business end of the gun and whack the attacker around the head with the other.-- po, Feb 21 2002 re Colt Model 1911 Pistol - a friend who is a Professional Shooter acquired one two weeks ago which was made in 1912 - it was in pieces when he bought it for $50.00. It is now the most accurate gun he has ever owned.-- thumbwax, Feb 21 2002 Supercat, After reading the part about opening the action cocking the gun, I realized that you are proposing almost the exact same mechanism used in double barreled shotguns, but with a hammer as a safety. Aren't you?-- Krate, Feb 21 2002 What use is a gun that can't kill? (sorry everyone, I should just leave this well alone - I'll stop now)-- mcscotland, Feb 21 2002 Po that is a terrible idea. Hitting someone with a derringer's butt might well set it off, shooting you in the hand. And really, do you want to HOLD THE GUN TOWARDS HIM SO HE CAN GRAB IT AND SHOOT YOU?!?!?!
As for the idea, it sounds quite reasonable, assuming Derringers are your thing. There are double action derringers in existance now though, so this might be a bit irrelevant.-- Madcat, Jul 23 2003 Who needs derrimgers when you can holster a Walther PPK? Nice and small, deadly, cool looking. Or you could throw stealth to the wind and just carry two Desert Eagles, you wouldn't need a derringer with that kind of deterrent strapped to you...-- whatastrangeperson, Dec 22 2003 random, halfbakery