Yet another reason to love Glocks. The base gun is my Glock 20. I bought a used Jarvis conversion barrel from GT that allows me to shoot .40S&W through the gun using the same G20 magazines. Then I bought a used G21 upper, also from GT, slapped it into the frame with no problems and now I can shoot .45 ACP. I just shot it the other day and it shoots like new. <a href="http://photobucket.com" target="_blank"><img src="http://i178.photobucket.com/albums/w275/x_revo_x/sports/Glock20-21.jpg" border="0" alt="Glock 20, .40$&W Conversion & 21 upper"></a> Three calibers using one base gun and all of this with no gunsmith fitting necessary at all. With the G20 upper, one can purchase yet another conversion barrel in .357 SIG. With the G21 upper, one can puchase a conversion barrel in .40 super, but that's being esoteric now.