Double Down on Reliability. Invented by Jim Sullivan, one of the original designers of the M16, the SureFire Optimized Bolt Carrier (OBC) doubles the reliability of any M4/M16/AR variant weapon system during suppressed and suppressed firing. Its patented design allows more time for reliable feeding of ammunition from the magazine and nearly eliminating bolt-over-base malfunctions. The OBC also delays unlocking of the bolt during the firing sequence, which allows expanding gases more time to exit the bore, in turn reducing back-pressure gases exiting the upper receiver group. Additionally, the neutrally balanced counterweight improves carrier and barrel extension lock-up, nearly eliminating bolt bounce. The OBC reduces felt recoil for better target tracking and greater weapon control when firing. Coated with an advanced anti-friction coating, the OBC resists friction during use and makes cleaning easy.