A short-length, belt fed machine gun for convenient use includes: (A) a receiver having a length in the range of about 17.75 inches to about 20.3 inches, (B) a barrel assembly, and (C) a gas cycling assembly. A gas port of the barrel assembly has a width of between about 0.063 inches and 0.200 inches. The distance between a center of the gas port and the breach of the barrel is between about 7.605 inches and about 9.395 inches. The gas cycling assembly features a unique polymer kinetic energy dampener assembly located longitudinally rearward of the operating rod, which is useful in achieving a desired cycle rate of the gun (e.g., about 600 rounds per minute (RPM)) and in minimizing muzzle climb. A unique mounting bushing selectively, removably mounts to the gas cylinder in order to achieve a shortened gun with many of the advantages of conventional longer weapons.