I know the little Jennings J-22 is (by me even) regarded as pot metal junk...which leads to a story.
After having several (thinking they are supposed to work), I found one that did.
One that actually had rifling in the barrel and did not go off when jackin' a round into the chamber. (that's 2 down, so far)
At an outdoor range, some time ago, a friend showed up with his new TPH is SS.
Bottom line, he had malfs left and right and when it did shoot, he never hit anything!
Letting him try my "junk" Jennings enraged him all the more!
He kept 'em in the black at 25 yards and he was 70 years old then.
Generally, IMO, .22's that small give up some reliability and accuracy...not to mention velocity, after all, the cartridge is called a .22 LONG RIFLE.
.25 autos can be found in a smaller package and some are old classic pieces...Baby Browning, Colt and CZ Duo, for example.
I agree with cyanide on size/usability...but even the Beretta 21 I had sucked terribly.

I've got the Beretta 21A and it's a tiny little thing, I have the North American Arms 22 magnum revolver and it's equally as small.

[img]http://photos.ar15.com/WS_Content/ImageGallery/IG_LoadImage.asp?iImageUnq=93[/img]

The nice thing about the Beretta is that it actually works and costs almost $200. I can't recall mine ever jamming on me with the thousand or so rounds though it. It's carried by my wife while camping as she's a tiny thing and has a really tough time racking the slide of a fullsized semi-auto.