If you choose to swap an empty RPG for another weapon, the RPG suddenly has a rocket attached to it when you set it on the ground and pick up the other weapon. (You cannot have an empty RPG that is silver because the silver weapons have unlimited ammo).
If you put a silencer on a weapon and swap it for another weapon, the weapon you got rid of is laying on the ground without the silencer on it. This is reversed with the MAC-10, in which you take the silencer off, swap it and it appears on the ground with a silencer on it.
Muzzle rize is not properly shown on several fast firing guns.
The UZI's action does not move externally, unlike what is shown in the game.
When you insert a clip into a gun in the game, the bolt closes automatically. The bolt is actually supposed to stay open until you cock it shut.
The MP5 features a roller locking bolt mechanism with an internal closed bolt firing. This means the bolt on the left would not move while firing. And you have to manually lock the bolt back it doesn't lock on its own.
The M16's charging handle doesn't move. It has an internal closed bolt.
Most of the weapons have an exaggerated magazine capacity, but this is deliberate in order to emphasize the action of firing a weapon and that the user can't do that if they are reloading.