I would go ahead and change the casings coming out of the rifle to be more erratic and faster, the part when the ejector throws the casing is all the same. But once the casing starts to travel through the air they tend to be more erratic. When the weapon starts to get hot the casings start to take on different trajectories. Also add some spin to the casings once they leave the chamber. I think a little variety would look really good and less man made. As of the textures I would add some scratch marks and scuffs, make the metal look worn and the same goes for the wooden grips. Also when the casings hit the ground have them bounce and rotate a little bit and then fall to the ground and stay put. Watch black hawk down or any new action movie to see them fire those types of weapons. I hope this helps.

https://www.sovietarmy.com/small_arms/ak-47.html