freely downwardly through the bore of the nipple 8 additionally the sealing plug 20 is provided with a plurality of external molded annular seal elements 30 for effecting a sealing engagement with the seal bore 8a of the special nipple 8 thus the sealing plug unit 20 and the perforating gun 10 may be lowered to the position shown in fig1 a and 1b where the perforating gun 10 is disposed opposite a production formation pf the perforating gun 10 is then discharged in this position by any conventional firing mechanism 10 mounted on the top of gun 10 such as by fluid pressure or the dropping of a detonating bar downwardly through the unobstructed bore 5a of the production conduit 5 after discharge of the gun 10 resulting in the formation of the perforations 2a in the wall of liner 2 the work string 6 is raised so as to pull the discharged perforating gun 10 upwardly through the latching nipple 8 and to permit the sealing plug 20 to move upwardly within the nipple 8 to the position illustrated in fig2 b referring now to fig3 a and 3b the construction of the sealing plug 20 is shown in enlarged detail it will be noted that the sealing plug 20 comprises a solid central body portion 20a to which a connecting sub 21 is shearably connected by shear pin 21a connecting sub 21 is provided with internal threads 21b for effecting the securement of the connecting sub to the bottom end of the perforating gun 10 central body portion 20a is extended downwardly.