A cartridge assembly for use with a surgical stapling instrument, the cartridge assembly comprising a channel, a cover configured for mechanical engagement with the channel, a staple cartridge configured for mechanical engagement with the cover, and a knife configured for translation with respect to the cover and the cartridge；wherein the channel includes a protrusion for engagement with a blocking member of the cover； such that upon engagement between the channel and the cover, the protrusion causes the blocking member to move from a first position where the blocking member is substantially parallel with a plane defined by a surface of the cover, to a second position where at least a portion of the blocking member is spaced from the plane of the surface； and wherein in the second position, the blocking member is configured to substantially prevent distal translation of the knife after the knife has been deployed to fire staples, and then translated proximally past a predetermined position.
