Most probably because you pressed the crouch button (ctrl). The thing is, this doesn't make you go lower, I need to get a player model with animations first. For now crouching only increases accuracy, decreases recoil (how much depends on the weapon) and stops you from walking. The crouch upwards recoil for G36 variable I set to 0. A bit unrealistic, but I did it to show that you can set these variables are flexible and can vary from weapon to weapon.
Everything looks great,in my opinion,except that the weapons shoot too fast for 1-2 seconds I can empty the clip/magazine(dunno the exact word ) It is realistic,because in reality the weapons now shoot very fast , but you dont want to get out of ammo because you were surprised by an enemy make it a little like Counter-Strike in that part and it will look better.
Yea the rates of fire aren't realistic, I still have to calculate them with time etc.
The thing is, the rate of fire will ultimately affect the pace of your game. I have to decide that but it should be pretty fast. And it should also be a factor to balance out the weapons.
Changing it isn't a problem though, it's just a matter of a few variables.
Just to let people know... I need a modeller/animator to do the player models, and this is for free (as my whole game is). If anyone wants to step up and do this I'd be happy to accept (I'll need to see some work first though).
Just some number: An Ak-47 shots at 600 RPM, so 10 shots per second...them you can empty the magazine in 3 seconds! The French FAMAS shots at 900 RPM ! so 15 shots per second...empy the magazine in 2 seconds !
I have researched many technical informations on modern the weapons...i have implemented all this in my demo. Not good graphics, but itīs a very realistic simulator.
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so it ain't smooth if it ends too early 
) It is realistic,because in reality the weapons now shoot very fast , but you dont want to get out of ammo because you were surprised by an enemy 