Jerusalem pet-shop supplier Tai Nizar picked up a 9-millimetre semi-automatic pistol, weighing it in his hand. At just 620 grams, it was light and compact and sat comfortably in his palm. Mr Nizar, a Jewish Israeli, was shopping for a gun smaller and more easily concealed than his current weapon, so he could defend himself against a new wave of violence in the region. He pulled his sunglasses down over his eyes and squeezed the trigger. Five shots rang out, piercing through a paper target hung in front of a rocky hill, at the sprawling Caliber 3 counterterrorism and security...