How many rounds you could shot before next rifle cleaning? I put 300 yesterday on previously cleaned rifle and cleaned it this morning again, however I didn't find many parts dirty and am shooting brass only ammo. Is it safe to shoot 500-600 rounds before cleaning it next time? M&P15 is slight pain to clean, lot more parts and places in compare to my other rifle and shotgun. In another hand I am impressed with accuracy, low recoil and how compact and light this rifle is. Just cleaning is a pain 
