The noise/flash problems with the XM177e2 were mostly related to the old ball powder used in the M193 ammo. The same problem that led to jams in the M16 system. And even though there were fewer reports of CAR15's jamming, this could just as well been a mix of improved maintenance or the fact that there were fewer CAR15's in country.
The flash/noise supressor in the Colt Commando has several channels to indeed supress the muzzle blast. These channels apparantly got clogged with calciumcarbonate rendering the device nearly useless.
The weapon was used by LRRP units, SEAL teams, Airforce FAC teams, MACV Studies&Observations Group(SOG), Green Berets, and selected infantry personell(mainly RTO's, NCO's and officers). Strange enough a large number of REMF's used the XM177E2 riding on the "special status" the weapon gained. Leaving short supply to the operators in special ops.
The XM177E2/CAR15/Colt Commando was used well into the late eighties when it finally was replaced by the M4 carbine for it's intended purposes.
edited to add pics Note the 11.5" barrel with the noise/flash supressor, the telestock was aluminium at that pointcuttrough of the flashhider shows the channels, now you can imagine what would remain of the funtionality if these become cloggedKuiper