This has probably been addressed before but I did a search and could not find anything. I have a Gen 3 21SF and thinking about going to 10mm. I believe the lower parts are the same and I just need the entire upper slide, barrel and spring in 10mm. As far as the magazine for 10mm, will it fit in the lower like the 45 magazine? If this is possible which Generation upper in 10mm do I need? If this has been mentioned in a previous thread please direct me to it. Any help will be appreciated. I might add that I'm interested in purchasing the entire upper so that I can easily change from one caliber to the next without replacing extractors.