A fixed stock adapter for a receiver of a fire arm comprises a receiver engagement portion disposed at a top end of the fixed stock adapter that further comprises two opposing sides configured to couple to a portion of the receiver of a firearm. A transition portion of the receiver engagement portion is configured to contact a portion of a fixed stock accessory and be congruent with the portion of the fixed stock accessory. A spine is further configured to couple to the two opposing sides and the transition portion. An accessory engagement portion is coupled to the spine and comprises one or more accessory engagement surfaces configured to fit within the fixed stock accessory and at least one coupling feature configured to receive a coupling element. The coupling element configured to engage a coupling feature on the fixed stock accessory.