Got a crazy question...maybe. Some background...while talking with a prepper buddy on mine the discussion came up about firearms (imagine that) and the availability of parts, ammo, etc. Something he mentioned got me thinking...he has a Glock 23 and a 1911 with different uppers for the Glock...9mm and 22. His #1 reasoning for these two guns...as you know parts can be swapped across the board with each model and parts are plentiful or will be. His #2 reason...if the SHTF these 4 caliber will be more plentiful than others, so...I'm not a Glock guy...stupid questions to follow...can you shoot 9mm through a G23 with just the top end swap? Can it be done in the opposite direction...G17/19 would you be able to shoot 40S&W with a top end swap?