I got this for my Birthday and it's amazing. It comes with a metal mag. You can use it for most anything. fits 16 bullets in a mag. Shoots .12 nicely, but haven't tried .20.(their probably better).
I'm just gonna say this gun is not that bad for 40$. I have had it for about a year and the best part is its gas consumption. This thing uses very little gas and doesn't look that bad. i found that it was very durable for plastic based off how many times I have dropped it but don't try it :). It has around 400 fps and hurts when shot by it. It is very accurate and worth being a quick side arm so buy it!