This will screw onto a 16" barell but the threads are set forward to make it appear to be a 11.5" bbl with a 5.5" FS.
Kind of a neat item for a M4gery. $20 shipped
FYI, The hat and Glock 33 round mag are FS as well. $10 on the hat, size 6 and 7/8
$45 shipped on the Glock factory mag