In our line of business where we engrave on AR-15 ejection port covers, the question often arises of exactly what is the “inside” of the port cover versus the “outside” of the port cover. So here is the official answer. The “inside” of a port cover is the side of the port cover you will see when the port cover is in the open, or ejected, position. This is the position the port cover will be in after your AR-15 has just fired a shot. The “outside” of the port cover is the side of the port cover you will see when it is in the closed position. This youtube video further explains the sides to a port cover: