A plasma rifle accelerates a fist sized bolt of superheated plasma containing a tiny amount of anti-matter. This gas-projectile moves between eleven and thirty kilometers per second, or more than thirty to sixty times the speed of sound. On impact, the anti-matter annihilates, producing a blast of heat and hard radiation in addition to a shockwave as the air expands.
In a real fight, you do not want to get hit by one of these weapons. They will remove your arm or your legs before the sensation of pain reaches your brain. A direct hit to the torso will spray half of you in one direction and flash fry the rest. DO NOT fucking get hit. If you are taking fire, find cover. If the plasma is eating through your cover, fall back.