That bites...but good news that no one was injured.
Still stinks that your AR is down. Hopefully it is something easily fixed with no replacing of parts. This is another reason that I've been contemplating picking up one of those DPMS Receiver Rugs:
I always thought they might be a gimmick or something. But after reading posts like yours, it might be worth a shot. Even if you never needed it to work...that first time would have paid for it.
Thanks for the head's up on the ammo.