A slideable ejection port cover having at least two configurations, an open configuration in which shell ejection via the ejection port is enabled, and a closed configuration in which the ejection port is substantially immovably covered; the ejection port cover comprising a shutter operatively connected to a locking component, the shutter slideable along a longitudinal axis of the receiver; wherein the locking component comprises a spring configured, at such times as the ejection port cover is in the closed configuration, to hold the locking component in a pressure-applying mode against the receiver, the pressure-applying mode being a default mode, thereby immobilizing the shutter relative to the receiver, and the locking component configured to compress the spring when pulled manually away from the receiver, thereby enabling reversible transformation of the ejection port cover from the closed configuration to the open configuration.