I've never shot one. Although it's frequently reported as having a 22 caliber bullet in a necked down 9mm brass, that's not true. The parent brass is actually a moderately shortened 223 Rem or a mildly shortened 221 Fireball. According to this website, it pushes a 40 grain, 0.224" bullet at 2000 fps from a 5" barrel. What's is for? I guess one could use it for shooting vermin using an 1911 or for making an 1911 into a cheap man's 5.7x28.
ETA: Forgot the LINK
This post was edited on 2/13 at 9:19 pm