When comparing a lot of compact and sub compact pistols, it seems that the 9mm versions are as big and have as long of a barrel as the .45s. Now having shot .45s for years, and teaching others, the recoil of a .45 is not bad. It's not nearly as bad as a lot of people make out. In fact it is not something that should affect the choice of pistol caliber. So why do a lot of people choose a 9mm when they could have a .45 the exact same size & length? I've been researching the actual sizes of pocket guns and compact guns. Except for the Rohrbaugh and Kahr the .45 versions are just as small as the 9mm versions. Somebody please explain to me why a smaller bullet is preferable when you can have a .45. And what about the .40? Why choose a 9mm over the .40 in the same size gun. Note that I'm talking about small concealable defensive guns only-not target guns or full size duty pistols. Yes,I realize I'm opening up a HUGE can of worms but am curious about this.