But law-enforcement officials and gun owners say the advanced ammunition is the perfect bullet to stop a criminal in his tracks without passing through to hit a bystander.

"There is no magic bullet, but this is about the closest thing to it," said Col. Leonard J. Supenski, a ballistics expert and chief of technical services for the Baltimore County Police Department.  "It has the stopping power that police officers need and it is less likely to ricochet or go through the bad guy. As it expands it dumps all of the kinetic energy of the bullet into the target."