If you have a glock23 how hard is it to buy a 9mm barrle for it and clip to change out the cal. is it possible???Is it reliable? Can you go the other way?? Say you have a 19 can you go to .40 cal with it?? How many have done any of this?? Looking at the .40 cal for the nock down power of it but like the idea of the 9mm for the cost of ammo for just plinking in the woods with the family.