Okay, it's true - this gun doesn't exist in Marathon. It's pretty amazing, anyway - and it shows some of the incredible detail Craig puts into his work. The large version (2000x1887, 1017k) lets you see things like the "Emergency Destruction System" label on the equipment behind the Marine, and the fact that the green text is actually just snipped from an email (which probably dates the picture's creation nicely). On his personal website, he's included these two 'in-progress' images (slightly larger versions available by clicking):