I'm looking at getting the 50 GI conversion kit for Glock 20/21, but I don't have the Glock to begin with. I have a conventional caliber handgun already, and want a .50 that isn't as big as .50 AE or .500 S&W. The way I see it, whether it's metal or poly I'm not too concerned (would prefer poly), but it would probably be cheaper to get just the frame than it would be to buy a G21 and then let the .45 slide and barrel just sit there.