X277 "Viper" Magnetic Rail Cannon

The X277 "Viper" magnetic rail cannon was a weapon that was displayed in the Museum of Technology sometime before the events of Fallout 3.

Background
The X277 "Viper" magnetic rail cannon was developed for the U.S. Military by West-Tek. Also commonly referred to as a "railgun", the weapon uses energy cells to propel depleted uranium round across a series of magnets discharging it at extremely high velocity. Deemed too costly to produce on a mass scale, the project was abandoned in 2044. The only known prototype was displayed in the Washington, D.C. Museum of Technology in 2077. As of 2277 its location is unknown.

Appearances
This weapon is mentioned only in Fallout 3.

Cañón de raíl magnético X277 "Víbora" Электромагнитная рельсовая пушка X277 «Вайпер»