9mm. Comes with the holosun 507, the compensator, 5 mags, and it's case. The Holosun is the 3 mode triple cross hair version in red. This is the Xr920 elite version but for whatever reason the slide isn't windowed, not sure why, I'm not the original owner. It is in fantastic condition, the pics don't do it justice. It was cleaned and oiled by me since i last fired it. 800 firm no trades