A railgun is a gun that fires metal projectiles (bullets) using a magnetic field produced by electricity. Unlike conventional guns, it does not use brass casings or gunpowder, and rarely needs to be cleaned or unjammed. Currently most railguns are experimental and are not used in war yet, but the U.S. Army is expecting to create one for war within the next few decades. In theory, a railgun could fire a bowling-ball-sized projectile fast enough to destroy a small building, even over long distances. Railguns are usually very large and not portable because of the need for a large power supply. There have been proposals to use the same technology for non-weapon purposes, such as aircraft and spacecraft launchers and specialized tools.