The E77 indicates Radom (Poland) mfgr. If there is not a WaA623 on top of the receiver then the rifle was built/assembled at Radom. The bbl & stock will most likely have the WaA623 proof, but could be something else because other bbls & stocks were used occasionaly.
What letter is under the ser nr? Where is this ai you say is one the right side - on the left end of the rec or"? How about a photo?
Sarge |