In the opening scene, the camera appears to be looking out a barrel (like many James Bond opening credits). The lands and grooves of the rifling are clearly visible, but a few scenes later the bullet is described as being unmarked by rifling, and the weapon is identified as an MP5 having polygonal rifling (no conventional lands or grooves).
During the opening scene with the poster taggers, the camera view is shown as inside the gun's barrel, then an explosion and a bullet is shown coming out and hitting one of the taggers. But even though there are spiral lands and grooves inside the barrel designed to spin the bullet as it is fired, the bullet the camera follows never spins.
Gil Grissom Photoshops the pictures of the 3 dead teenagers so as to be recognized. He puts on smiles and open eyes. When Nick Stokes hands the pictures to a man during the rap party, he hands him back the pictures, but the original ones...