I recently was given a beautiful 1952 Russian SKS as a gift. The only thing is it has one of those cheap looking aftermarket detachable AK style 20 round ( pinned out at 5 rounds) plastic magazines. I've been yet to fire the gun I'll be shooting it this weekend for the first time. I've noticed when the magazine is in I can't charge it, it won't close. Only when I take the mag out does it close. But does anyone know if this is a common thing with these guns and type of magazine? And will it close when the magazine is loaded? Also would I be able to replace this mag with the original 10 round built in magazine that SKS normally come with?