I've run into several instances in-game where my weapon model will disappear in the first-person view. The gun is still able to fire, and the reloading animation still works fine (you just see the hands moving). Switching to a different weapon and then switching back will usually fix the issue, although I have run into one instance where the gun model would not appear at all (this was with the rocket launcher, if I remember correctly).
I don't have any screenshots; I didn't think of capturing any images at the time, but the next time I run into this glitch I'll grab a screenshot and post it on here.