I think the problem with the vertical shells is the actual model itself is at the wrong orientation compared to the other shells, ie 90 degrees off, so that instead of lying flat on the ground at a random rotation, it is vertical with a random rotation (vertical axis) that you can't really see due to bullet symmetry..
Another thing you might notice with the M2 is that when you shoot a wall, it leaves two bullet holes
Anyway, I guess the casing thing isn't a huge priority, but I don't think it'd be difficult to fix