I am considering changing my handgun lineup and purchasing a few hk handguns.  My question is with a change of the barrel can I change the caliber ? I am sure I can if it is a 40, and change to 357sig, but can a 40 or 357sig be changed to a 9mm with just a barrel swap and change of magazine?  I am making the change from shooting glocks the past 12 years.  I am ready for something different.   Thanks for the help in advance!