I have a Pelican 1700 for my 16" bbl AR15 (w/ A2 stock). The rifle fits with about 1 inch to spare on either end. The quality of the Pelican case if first rate and the thing is built like a tank.
I also have a SKB 4 rifle/SG case (plastic w/ aluminum trim) , but I'm kind of dissapointed with the quality of it. The two halves don't quite fit right, and the locking latches look suspiciously like the "one-key-fits-all" type lock.