Abstract: An improved bolt, bolt carrier and barrel assembly for rifles is described. This invention provides bolt mechanism that has heavier lugs on each side of the extractor to distribute the forces more equally and reliably and thereby reducing firearm failure rate. Moreover, this invention provides a bolt system that is easily adaptable to different ammunition feed devices as well as different ammunition cartridges. This invention further includes a barrel having a barrel extension designed to mate to the symmetrical bolt head lugs of this invention.