the lower has collapsible dpms stock with everything esle standard on the dpms sportical 308. The uppper is a 16" chromomoly barrel with a quad rail and standard dpms railed gas block. The only upgrade that has ever been done to the bolt assembly is the upgraded extractor spring designed for the 308 extractor. Not to sure on the gas system length. Everything is stock on the rifle (dpms lr-308 sportical) except the quad rail and the spring that i talked about above.