http://www.heartsandminds.org/articles/childpov.htm
Yes, millions, 15 million to be exact. Read and learn.
As for the 20 rounds, its more accurate than M-16 and has a greater effective range than the either the M-4 or M-16. It also has a history of not jamming up as easily as either as well.
The extra four pounds means when you smash someone in the face they go down. I have been struck by both and M-16 and an M-14 and I remember the hit from the M16, the M14 knocked me out cold. If the extra weight makes you tired, hit the gym.