I noticed this while in the pregame countdown. When I was looking around and my teammate's player model went off screen, I would see their SVD vanish. The player model is off screen, but the long barrel of the SVD should still visible. But the moment the player was off screen the SVD vanished. I could make it appear and disappear by looking at or away from the player.

(forgot to take screen shots and shadowplay doesn't work with Sandstorm)
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I have not tested this in other contexts, eg whether the SVD barrel might be hidden when someone is firing from a window.
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Sorry if this has already been posted, I had a look for it but didn't see anything similar.