Anyway, I do not think it is realistic to shoot your weapon, aiming down the sights, while crawling forward/backward/side to side with good accuracy. How about a new crawling animation so that you cannot fire your weapon while crawling?
In the screenshots, all I did was just prone underneath a vehicle and held down crouch and you will see the "sprint" animation with the gun aiming downwards. So when someone starts to crawl, their weapon would be pointed downward and would be unable to fire until they stop crawling. The problem is the the weapon moves faster than the solder is crawling so that might be a problem...



