The present invention provides for a firearm having a receiver defining a bore with the receiver extending along a longitudinal axis. The receiver defines an ejection port transverse to the longitudinal axis with the bore defining an inner surface. The firearm further includes a bolt carrier disposed in the bore and moveable relative to the receiver along the longitudinal axis between a firing position and a rearward position. The firearm also includes a shield longitudinally affixed to the bolt carrier and movable with the bolt carrier as a unit between the firing and rearward positions along the longitudinal axis with the shield blocking the ejection port when in the firing position and the shield sliding along the inner surface away from the ejection port when moving to the rearward position in conjunction with the bolt carrier.