in one word: "clearance" shown with factory stocks, some aftermarket stocks are even thicker and provide less clearance HKS Safariland Can they fit? Yes Is it quick and easy? Not unless you practice a lot. One must very accurately and carefully insert the cartridge tips and try to line them up in the cylinder holes. While it may appear from the (slightly out of focus) pics that they're inserted crooked, there lies the rub, so to speak. They more easily line up "crooked" than they do "straight" due to the lack of clearance with the frame and stocks.