Lot of arguments here, I suggest you use what your comfortable with. I've used 10,20,30,60 round magazines and drums. They all worked. I even used one of those 100 round magazines and a beta mag. Now I'm not military anymore and never have been police roving around in a car. I'm a civilian now so I use a 20 round with my long barreled AR. But I occasionally shoot higher cap magazines at longer yardage just to keep in practice, you know for after the election!