Glossary : New York Reload
n.
A New York Reload is the tactical decision to draw a second gun instead of reloading the first. It is most popular in guns which require a lot of time and space to reload in the field. It originated in response to New York cops who would often carry a "Back Up Gun" and use it in a gunfight, as they were required to use revolvers at the time and seldom could afford to sit back and fuddle with a speedloader (and were known to treat their guns so badly that a malfuction was far from rare).
A technique similar to the New York Reload can be employed with derringers (essentially any small guns without a repeating function, usually cheap and powerful for the size, but with limited ammunition and very time-consuming to reload) and similar guns. However, as derringers are most often marketed to women or those who would otherwise hold concealment as the highest priority, carrying or needing multiple was seldom an advertised value. Add in the relatively rareness of derringers in a post-KelTec pocket pistol world, and you would see the relevance of such techniques significantly reduced. In fact, the creation and popularity of semiautomatics have made the concept nearly archaic.
It does, however, retain some utility to practice these days. Guns fail. While a critical failure with a semiautomatic or revolver is extremely rare, a squib round or a spring going pop can be problematic to say the least. This grows worse as you remember both Murphy's Law, and as you remember that most defensive gun use situations are high stress. A good many people still fire one-handed when the fit hits the shan. Or you'll have your dominant hand pinned or at a bad angle. A stovepiped cartridge case doesn't seem bad on the range, but when your blood is full of adrenaline, it's not so simple.
Carrying a backup gun and practicing a New York Reload is, to most people, being paranoid. The chances of being assaulted during your entire lifespan is far from certain in the first place, and the chances of a gun failure at that time are even less likely. Others find it better to have and not need, than need and not have, and a one in a million chance still sucks if you're the one.
And it's a fun way to put some more lead balls downrange at hundreds of feet per second. So, it's not like you lose out much.