Sorry to say but you are the one who has no idea . The notch is for the older P-88 ammo as it was still in use at the time . If you cover the notch with tape you can still load S ammo with the guide and clip . If you load the P-88 ammo in the rifle with the stripper clip you will see that the notch is exactly the same size as the round nose bullet and is beveled to guide it in . Also the period Germanicon military manual tells how to remove P-88 ammo from the en-bloc clip and put it into the Mauser stripper clip and load it into the 88/05 . But what would the German military know ???!!! As stated ALL Turk 88/05 rifles will be found with either the original .3208 groove barrel , a .323 updated German Z barrel or a Czechicon made .323 barrel installed by the Turks , PERIOD. The barrels are not " all over the place " , they are clearly marked as to size on the receiver and rear sight base . If you know what to look for. And yes I am the expert on Gew-88 rifles . You should look at about 200 real rifles and all the original German documents , not BS books by people who just made it up .