Can someone explain why the .40 caliber lost it's popularity? Searching the internet I can find no valid reason why the .40 has become so "unpopular", compared to the 9mm. Although I own none now, I've shot 9 mm and .40 cal. handguns and honestly couldn't tell a lot of difference in them. Seems like a .40 cal. can be bought cheaper than an equivalent 9 mm. Just wondering....