I guess you came across that effect already, too.
Almost all shooters have a static animation for weapon switching, meaning that the chamber of the gun is checked and cocked again and again, even when you shot it like T H R E E
I am turned off by it, so I suggest that the server keeps track of if you had the gun active already since spawn / pickup and if you have been attacked since (the gun could have jammed because it was bitten, jammed by spores or something like that).
If you 'checked into' the gun already, you dont have to and its ready that *tiny* bit of time earlier.
Also, rewatching the pre-alpha movie I'm not to impressed with the cocking animation for the pistol.
From what I could see it's sled is pulled back, but you usually dont aim at the roof to do that but in front of you (away from teammates ofc).