Only full automatic and semiautomatic firearms dump their fired cases at a crime scene.
Many firearms retain their empty cases after being fired.
Once any of these firearms is broken down, an emery board could remove the laser etching from the tip of the firing pin in about 5 seconds and not disrupt normal firearm use. I am, however, developing this technique further to allow the creation of miniature stamps, similar to those generated by the firing pin, which could be installed in many areas of the weapon to etch a micro-mark into the shell casing. As for the marking of the bullet itself, I have demonstrated that idea in principle and believe it can be accomplished. While, in its current, test form, the micro-stamp could be defeated by filing the firing pin, in the actual technology there would be multiple, minute markings. And I am quite confident that an emery board wouldn't do the trick.