First of all, I'm not too familiar with Magpul accessories, so this post will probably sound funny to some of you.
Anyway, not too long ago, I saw a 416 dressed up with Magpul accessories, and it had a handguard that sorta looked like
this, but it had rails on all four sides, and the one on top extended all the way to the rear of the upper receiver, sorta like those nitro-rails on the old S-System M4s (
these).
I'm fairly sure it would be a Magpul item as well, because I recognized the Stock, Sights, and Magazine as Magpul, but I have no idea what handguard it had, and I haven't been able to find a picture of it either.
It's probably not the best description, but if anyone has any clue about what I'm talking about, I'd be grateful! Just imagine if a Magpul PTS Handguard (I guess) had a baby with an M4 Nitro Rail, ha ha!