Derkwon Johnson, 26, of the District of Columbia, was sentenced today in U.S. District Court to 57 months in prison in connection with being a felon in possession of a loaded Glock 23 equipped with a machine gun conversion device, while he was on probation for two armed robberies, an assault, and other crimes. The sentence was announced by U.S. Attorney Jeanine Ferris Pirro.