Just to add to that. I just finished an AC comparison series and one of the blades used with all four types of razors was the Schick ProLine blade. It fit and worked in the Hawk V1 & V2, the brass Colonial General and the ATT SE1.FWIW, I never had any problem using the Schick Proline blades in my SE1/SE2. I wonder if it is an anomaly in the blades that you have? It seems odd that they fit mine and not yours. Have you done a visual comparison between your schick proline blades and another SE blade to see if there is any difference in the slots?