No, just the XM-177 moderator that had an inner baffle to reduce the sound reports a few DB's.
This slight reduction was to make the sound report of the shorter barrel sound of that of a standard 20" rifle, and prevent the reports of the rifles announcing that special forces were in the area.
The XM-177 had a 10.5 barrel, then was changed to the 11.5" barrel later on (XM-177E2). With the mod, both barrels are still shorter than the 16" allowed, which would require not only a Suppressor stamp, but a SBR stamp as well (if not a MG) on a semi rifle.
The reason for the 11.5" barrel, and the 5.5" permanently attached FS is to get the barrel to the legal limit for a standard firearm of 16". Granted that this combo is fun for short ranges due to the fireball that is thrown out of the FS, the short barrel really gives up velocity of the bullet. In average, you looking at bullet speeds from the barrel around the 2500 mark, and not the normal 3000 fps from a standard 20" barrel.