There's two; one's the 'autocannon' with the muzzle break, supplied by that belt feed in the back of its head, while the other is the smaller one with the P90-style magazine on its 'chin'.
This is definitely concept art for Keloid---a 'newer' version of the Keloid short film is up on the web and features a full-blown army of these things:
The pose is similar to the one in the Elysium robot pic, but there's subtle differences. Beck probably used the same pose reference, which is why they look similar.
