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 OR I will consider other even firearm trades of equal or slightly lesser value, as long as it catches my eye. I will also do an even trade for a Lenovo Legion Go, if you have one it could be your lucky day, i won't ask for any cash on top.