I don't believe it is. No images I have found or research I have done has ever shown a typical SKS mag well or anything close to it. I think this is just how they are.
https://www.google.ca/search?q=mc-5...ChMIwM_21ZTuyAIVT8tjCh0OkAio&biw=1366&bih=606
-Saryet, out!-
https://www.google.ca/search?q=mc-5...ChMIwM_21ZTuyAIVT8tjCh0OkAio&biw=1366&bih=606
-Saryet, out!-