The COP Derringer is a four shot double-action pistol in .357 Magnum, you break it open and load four cartridges, close it, then it's ready to fire four times. It's very compact, and with smooth lines to it, at a glance, it seems like a pretty cool idea, four powerful shots, right?
The reality is less amazing. To start with, this is actually a pretty heavy pistol, it's all steel, small sure, but very dense. An old police officer told of how he bought one back when it came out, thinking it would be a great backup gun to strap on an ankle holster, only he would soon notice that this heavy lump of steel on his ankle was affecting how he walked, he noticed he gained a strange gait from it, and it was uncomfortable. He eventually traded it for a much smaller and lighter pistol, a little pocket pistol in .25 Auto, which had no affect on his walk.
It's not a particularly 'good' pistol for what it is, the trigger is quite long and stiff, making it hard to fire rapidly and with precision, though precision goes out the window when you learn that each of the four barrels hit at four distinct points, they aren't actually 'regulated' together worth a damn, and hitting anything at near any range is quite difficult, the sights are practically for show. .357 Magnum is also incredibly loud and makes a lot of flash from a short barrel like this, and has kind of a painful recoil with this thing, shooting it with .38 Special would be nicer, but it doesn't improve the other things.
This would be a difficult gun to put to use past a couple of feet from the muzzle, and it was relegated to film and fiction, where its good looks was what mattered.
Here's a 1 minute video demonstrating it loaded and fired: https://www.youtube.com/watch?v=CKu0RXCB6G4