I don't know of any handguns small enough to fit into a petri dish. The handgun must be loaded and fired at the petri dish. A large caliber will be easier to aim since it would decrease the need for accuracy. Close range is a better distance. Shotguns and machine guns would do an even better job, rifles are fine. A sword decreases the likelihood of destroying a virus because of its low energy. Standing on a chair while wearing a lab coat makes you look cooler. Two hands can be used to aim the gun if it helps you. The handgun will not fire with the safety on, thus decreasing the probability of destroying the virus.