The perfect number.
Revolvers. Ubiquitious, classic yet modern. They've been around for well over a hundred years.
I think it's interesting to study the design of things to figure out why they were made the way they were. One of the most obvious features of any given revolvers is the number of rounds carried in the cylinder. With larger frames, it really is just a question of capacity... to a point, because the issue of where the lockup notch falls in relation to a cartridge becomes an issue. An even number of rounds means the cut is over a cartridge, weakening the cylinder. An odd number of cartridges means the cut is over "dead metal"... and an odd number will often fit better around the cylinder.
And that last clause brings us to the point of the post: How many rounds is right for as compact a revolver as possible?
1. One round does not a revolver, or repeater, make.
2. In *theory*, this can make the thinnest possible revolver. However, timing would be a nightmare as you need to rotate the cylinder 180 degrees, and with the compactness being an issue, it would be just as small and light to have two distinct barrels, and then... tada, derringer.
3. Now we're getting somewhere. Unfortunately, a 120 degree cylinder sweep is still difficult to time... anything over 90 degrees is going to be trouble, mechanically. And, you're going to leave a lot of dead metal between rounds.
4. Surprisingly this has been done... Colt's home defense revolver of the late 1800's had four round cylinders arranged in a cloverleaf. The "star" is actually a "square"... the easiest angle to check for. But, it has strikes against it... mostly because you actually end up with one of the widest cylinders possible, with the full width of the chambers diametrically opposed *and* standing proud at 90 degrees off the live chamber.
5. Ding ding! We have a winner. 5 cartridges arranged around a pin is one of the most compact and useable schemas. The cylinder sweep is 72 degrees, which is within the range of ease mechanically. the 5 cartridges means that the width of the cylinder is less than 4 or 6 due to the angle off the live chamber. Dead metal is kept to a minimum. It simply works, as millions of IJs and S&Ws and other pocket revolvers will attest. The .38 J-frame has been around a LONG time, and will be around for at least as long.
Now, I carry a S&W 432PD around the shop. It has *gasp* 6 shots. Why not 5, the perfect number? This is easy... 6 would fit. S&W wasn't about to change the frame and cylinder dimensions for a single model, and 6 .32 cartridges easily fit in the space that 5 .38 cartridges would. If you note the length is also the same as the largest of the J-frame chamberings, the .357 Magnum. That call was about economics.
if S&W wanted to, they could make a truly *tiny* 5 shot .32 H&R Magnum revolver. But why? The J-frame is small enough for nearly anyone to conceal handily.