A configurable blowback bolt system is provided. Embodiments include a two-part configurable bolt assembly having a bolt carrier and a configurable bolt that allows for use with various calibers of ammunition, both rifle and pistol. The configurable bolt may also eject cartridges to the right or left side of the rifle by moving the extractor to one or the other side of the bolt. A buffer may be included as part of the configurable blowback bolt to shorten the stroke based on the caliber of ammunition being fired with the configurable blowback bolt system.