And for what it's worth,
1) I've never seen anything designed to attach to an AR-15 that will hold 100 rds,
1b) (I realize that you are criticizing the media over this.)
2) I've never had any trouble putting holes in things at 300M even with open sights
3) Except for one bolt-override, in thousands of rounds, I've never had one fail, as long as it was kept clean. 100 rds is not enough to dirty it up enough to fail in an engagement.
4) Full-auto is a waste of ammo. Even in an intense firefight - ESPECIALLY in an intense firefight - I would never use full-auto, unless I was using a SAW with a number of 200 rd magazines handy.