You'll also need gas, most likely HFC22 (green gas), silicon lube, and BB's. This IS a gas gun, so it functions just like a real weapon, blowing the slide back every shot, and chambering the next round. If you end up picking this up, make sure that you fill the mags upside down. Thats just how gas guns work.
I appreciate your reply. The reason I asked about the 20/21 specifically is that they are a slightly different frame size than the 17/22 to accomodate the .45ACP and 10mm rounds. Since I'm buying this as a DT training tool, I wanted the grip and such to be as exact as possible. If I have to use the 17/22 size frame, it won't be the end of the world though.
Ah, my bad. I feel like an idiot now ;g . I think that the g17 size is about as close as you're going to get. If you have any gas gun related questions, feel free to email me at zgulsby at cox dot net, or hit me up on AIM. MY sn is "LOXOSCELIC"