I have a Glock 21 along with the normal Glock 21 parts. I also have a Glock 20 barrel,recoil spring assembly, and a few Glock 20 mags. I am curious if I were to buy and swap out the 45 ACP ejector with a 10mm ejector if I would be able to install my Glock 20 barrel, heavier springs, and 10mm mags and use the Glock 21 in 10mm? I have been planning to buy a Glock 20 but as always money is too tight to just keep buying more and more guns. I need a smaller CCW but I am going G26 or G27 as the G29 is just bigger then I want for a light CCW weapon. I figure if I can get the G-21 to shoot 10mm it is an extra cartridge for me without a huge investment. Thanks for any advise!