Weird Arm glitch with M4A1

[GoldenRetriever 1]

Noticed this while playing on an Overwatch server with my friend after he picked up an M4A1, Anyone ever seen this and if so, how do I fix it? 

 

Thanks

[Steak and Potatoes 13480]

Try a screen flush, hold left shift and - on the num pad then type in flush.

[CornProducts 315]

Steak is right, although just to add to his response, you won't see a text box or anything show up, you just have to type it in and assume it is right. If you did it correctly the screen should go black for a brief second and then come back all nice and clean.