"The AR-15, the semiautomatic rifle used at Marjory Stoneman Douglas High School in the deadliest high school shooting in U.S. history, uses bullets that can cause softball-sized exit wounds, leaving behind a significantly larger trail of mangled tissue compared to handgun bullets. For trauma surgeons, the injuries are harder to repair. For victims, the chances of survival are lower...The AR-15 and similar rifles fire bullets at a speed of about 2,800 to 3,000 feet per second, compared to a 9 millimeter handgun, which fires bullets at a speed of between 700 and 1,100 feet per second, according to Dr. David Shatz, a trauma surgeon at the University of California, Davis...Shatz said bullets cause permanent cavities, where tissue is destroyed, and temporary cavities, which are areas around the permanent cavity that open up for a fraction of a second because of the “sonic force” of a bullet. Cavities caused by bullets like the .223 caliber bullet typically fired by the AR-15 are much larger than the cavities caused by handgun bullets."