From Bearing Arms:

As the New Jersey senator and Democratic presidential contender explains, “Microstamping is technology that allows law enforcement to identify the source of ammunition used in crimes by making a shell casing traceable to the specific gun that fired the round.” The problem is that such technology has not been developed yet in any practical and cost-effective form. So when Booker promises he will “fight to require that microstamping technology be incorporated into new models of semi-automatic handguns sold in the United States,” he is actually promising a moratorium on new handgun models until that dream becomes a reality.