I was just thinking of getting a 640 pro and buying a 9mm cylinder so I have two calibers. I can carry it as back up to my glock using 9mm ammo or my Smith Model 19 with 38 spl +P if I want. Could it be that easy? If not a pro then a 640 with a new springs, cylinder smithed to take full moon clips (80.00) and a trijicon front sight (80.00). Ideas?