That link says the barrel included is 7", but those don't look like 7" at all....
http://www.pbase.com/racingmaniac/image/141064289
^ that is a Prime 7.5" barrel on a 7" KA Larue rail, the threaded tip basically is all that sticks out the RIS.
Feeling advanturous, you can get a 7.5" outer barrel, as long as its heavy profile, and cut and rethread it to your length....