The following gun sketch is of an ACR - the Remington/Bushmaster "Adaptive Combat Rifle". I think that it is a decent sketch, although it was somewhat difficulty to make given that the image I used was exceedingly blurry. It turned out well, nevertheless. This gun is, like the others that I have sketched, one from Call of Duty: Modern Warfare 2.
I hope that you like it, feedback (positive or constructive criticism) would be appreciated!