Glock 21 in an SBR stock. ATF designates the pistol as a short barreled rifle in this configuration.
Save those thumbs & bucks w/ free shipping on this magloader I purchased mine http://www.amazon.com/shops/raeind No more leaving the last round out because it is too hard to get in. And you will load them faster and easier, to maximize your shooting enjoyment. loader does it all easily, painlessly, and perfectly reliably
KPOS A kit made by Zahal of Israel, it converts your clock into a compact PDW (Personal Defense Weapon). Keep in mind that your Glock will essentially become a SBR (Short Barreled Rifle) and has to be registered as such with the BATFE.