I bought one.  I like it, but it didn't fit right.
See:
http://youtu.be/vTSWcnqyqSQ?list=UURVvWx5JBdbCKq7brtedsQA

Have you contacted AP Custom or Brownells? I've only installed three of those handguards so not a huge sampling, but all three fit well. Hope you get it straightened out.

I had no problem installing mine...

I tihnk they are really nice, it just didn't play well with my XLP piston, contrary to what Adams had published.  Too bad, it was a really nice FFHG for the $$$.

It is a real nice handguard, very light, and every other part about it fit well. Someone else suggested my barrel nut was too big. They BOTH were?? (from different manufacturers??)

It would have been more hassle to send it back, get another one, and find the same problem again,  than just do what I did.
As the video shows, I had to grind off the tops of the teeth on my barrel nut to make it work.
Taking off a little metal is no big deal, just shouldn't be required to make something work as it is supposed to.

I did send an email to AP Customs (to alert them of this problem) but got no response.
As I said, I do like it (the handguard minus the aluminum mounting hardware with a polymer laser rail attached is only 2.9oz), and I would buy another.
Just wanted you guys to be aware of this issue...

Here is a pic (without the mounting hardware) but with a polymer laser rail:

http://s1119.photobucket.com/user/FunWithPaul/media/DSCF0659_zps6e8e3fb5.jpg.html

My 2 AP CF hand guard fits standard barrel nut without any issue. Give AP custom a call, their CS is excellent as I know.