I just purchased a Glock 21 chambered in .45 and it is my understanding that I can basically chamber the gun in anything between 22LR and .45 by simply changing magazine, and barrel, with the exception of .22LR in which case I would also need to change the slide and spring. Now that I know all of this I just need to figure out where to get the parts... I suck horribly at tracking things down on the internet and Google does not seem to be in a very helpful mood tonight. I only have 3 calibers that I am interested in with this gun. 9mm for plinking or for when my girlfriend needs to have the gun for any reason. 357 sig just because I have never used that caliber and i have an extra space for a couple hundred more rounds in my gun safe for a different caliber and then obviously .45 for me whenever I am keeping the gun for myself. for the 9mm conversion i would LOVE to lay my hands on a threaded barrel that will accept a compensator. They really help keep you on target and reduce muzzle climb. i must have it for plinking purposes! Once again I have no idea where I might locate any of these conversions. Sorry for such a long-winded book for such a simple question. Where could I find these conversions for a glock 21? 9mm threaded barrel that will accept a thread on muzzle compensator/brake (and maybe a glock 18 type 33 round mag), and a 357 sig regular barrel or ported barrel if I am lucky. I am not sure if the spring needs to be changed with these conversions either. Please let me know. I just want to locate everything I would need to put 9mm and 357sig down range with the same handgun.