Hello.
I believe with all things considered this may be a very simple process to make possible in game.
I have watched many videos about how to mod an SKS in real life to take a 30rnd akm magazine.
It only requires the quick application of a screw driver and vwala, the 10rnd integral magazine is removed and the SKS can now be loaded with a 30rnd akm magazine.
Obviously someone will only want to do this when they have a 30rnd akm magazine, seeing as even loading a single round will not work after applying a screw driver.