The California Senate has passed a bill that would require all semi-auto handguns sold by 2008 to have micro-stamping technology that will stamp spent shell casings with a code that will supposedly link spent shell casings with the gun that fired it.  This technology is meaningless as a crime prevention tool.  The fine metal imprinting head located on the firing pin will be subject to much abuse and wear.  A gun that has had many rounds cycled through it might lose the ability to imprint either through wear or a build up of residue.  The system is also subject to user modification.  The imprinting parts can simply be replaced or modified