I am sorry if this has been already covered, but I am considering purchasing a Gen 4 Glock 21. Am I correct in that I can purchase a Glock 20 slide and barrel and that it will work with the Glock 21 frame ??? Also am I correct in that I should be able to purchase a .357Sig / .40S&W conversion barrels and use it in the Glock 20 slide. Please let me know if this is correct. Thank you for any info. God Bless :supergrin: Wanna kill these ads? We can help!