“I thought, ‘This is stupid,’ ” Joshua Clower, 40, recounted recently, standing beneath a canopy of pines on the agency’s gun range. He had hoped the chief would drop the idea, but when that didn’t happen, Clower grudgingly began research, mostly seeking to debunk it. He called a respected doctor in town who thought the strategy had promise. He reviewed police shooting videos that showed chest shots did not always immediately stop a threat. Some people were able to keep advancing, while those hit in the leg or pelvis usually couldn’t.