I thought I had this figured out but am now concerned that this may not be legal. I have a Beretta 1201-FP with a non-removable mag that has a 5 round capacity. I am planning on putting a pistol grip stock on it, but some people have the idea that this would not be in compliance with 922r. I don't understand how it would be any different than current Benelli M4's...and thus how it would be illegal.