If you change from gun to pistol, your character puts the gun slowly on his back like for a march and pulls out his pistol.

In real life, if you have to switch fast to your pistol in any situation you just drop the gun, which can not fall to the ground because it hangs on the carry belt and pull out your pistol.

So you end up with the pistol in your hand aiming towards the enemy and your main gun is hanging down on your right side aiming to the ground.

Not as now in game with the gun on your back, aiming up to the sky ...