Another day, another big swing in the shares of Taser International ( TASR) Shares in the stun gun maker surged Thursday after the Defense Department reportedly backed the safety and effectiveness of its stun guns. A Pentagon spokesman said Taser's public statements about a government study commissioned to test the safety of the devices accurately represented its conclusions, according to a report in The Wall Street Journal. The company Thursday also released details of a medical study that concluded its technology posed no cardiac risk. The Arizona-based company results published in the Pacing and Clinical Electrophysiology Journal concluded that the NMI electrical discharge from its guns showed "cardiac safety" and that the devices "may be safely applied multiple times if needed." Earlier this month, Taser disclosed an informal Securities and Exchange Commission inquiry into company statements about the safety of its stun guns and a recent order. Taser's guns have been the subject of rampant media controversy due to the number of people who have died after receiving shocks administered by police. The company says its guns were not responsible. Taser's weapons are used by about 6,000 law enforcement agencies around the world. Taser quoted the journal as saying the "devices have been empirically determined to maximize neuromuscular stimulation, cause pain and muscle contractions and temporarily incapacitate a human subject. Shares rose $4.29, or 25%, to $21.30 in premarket trading Thursday. Shares fell almost 30% on Tuesday after the company confirmed a round of recent insider selling and said competition could slow deliveries. The stock has been one of the market's best performers since 2002 but is down sharply this year, having closed at $31.65 on Dec. 31.