A .22 magnum isn't nearly the same as a .223 (5.56mm) round. Yes, it's similar in caliber (differing by .003in), but the conical shape of a 5.56 gives it different ballistics due to the fact that it handles differently (better) at supersonic speeds. However, there is a handgun out there that comes quite close. the FN Five-SeveN fires a 5.7x28mm round that is designed to pierce armor. However, the AP rounds are restricted and civilians can only purchase the hollowpoint and ballistic tip rounds. I own one, and it is a
joy to shoot. It is one of the most accurate handguns on earth, and it is capable of hitting targets at 100yds with a skilled shooter behind it.
Why won't you see them in the hands of the average criminal? They are EXPENSIVE!!!! They are ~$1200 each, so law-abiding citizens can barely afford them most of the time, and the ammunition is also quite expensive at ~$22.99 (for 50) minimum and up to ~$56.99 (for 50) max. It all depends on where you get it, and it's not exactly a type of ammunition that is commonly sold at Wal-Mart either. It must be ordered or come from a larger retailer.