I have a lightly used KKM Precision conversion barrel for a Glock 20 (see link below). This is a quality barrel that will allow you to shoot the much cheaper and more readily available 40 S&W ammo from your Glock 20. All you have to do is drop it in and load your standard Glock 20 magazine with 40 S&W and you're good. It's that simple. http://www.kkmprecision.com/custom_pistol_barrels/product.php?productid=26&cat=16&page=1 I'm asking $125, shipped. Thanks for looking.