The gene gun, or biolistic particle delivery system is a crude but effective way of inserting new genes into cells (usually plant cells, because of their thick cell walls) the required DNA is coated onto the surface of 1 micron diameter gold or tungsten beads, which are then placed in front of a plastic bullet in a specially designed gun. The bullet is fired, either by an explosive charge or a blast of compressed gas, and the beads fly down the barrel at a metal plate containing a microscopic hole, behind which the target cells are placed. Some of the DNA-covered beads from this will pass through the hole, and hit the cells at a speed sufficient to pass through the cell membrane and into the cell. The cell membranes will heal themselves, and the DNA will be successfully inserted into at least some of the cells.
It was developed by plant scientist John Sanford in 1983, when he thought of using a BB gun to get through the thick cell walls of plants.