I would have to say 9 mm at least I Carry a 92fs

Ballistics will show that a 22 will penetrate ballistic gel nearly as far as any other bullet but it doesn't pack as much "punch" as larger calibers or leave as big a hole. My coworker tells me if you have to use it, you'll want to be able to deal a death blow (ie large caliber) I feel that a 22 is adequate if you are confident in your aim. History tells us a large man will keep coming after receiving several shots from a .38. That's why the U.S. Army switched to the 45. Bottom line though, any caliber is infinitely better than no caliber.

The main consideration is to have something you shoot competently, and that you can carry comfortably at all

I am looking for something to carry and I'm a big fan of shooting the PPK 9mm. I think a 9mm is plenty of "punch" and a 45 is usually pretty big even in carry size. Also, a .380 is easy to shoot like a .22 and has little better stopping power than .22.

I carry a Walther PK380. Easy to conceal. 8+1. Right or left hand safety. Have yet to have it misfire or FTE.

Listed on or in most gun magazines and the American Rifleman the CDP is listed with the three sizes available. The Ultra Carry is light weight, accurate and a fine piece, in my opinion, and we all know what opinions are like.