Shawn did an interesting accuracy test on a Colt 14.5 inch M4A1 SOCOM barreled upper of mine a little while ago. His results can be read here.
Here is what a Colt M4A1 SOCOM barrel looks like new in the bag:
Note the cardboard wick in the barrel.
This picture shows the yellow dot of paint found on new Colt barrels. Also note the flats in the heavy barrel profile and notches in the handguard cap required for mounting a M203 grenade launcher.
Colt AR15 barrels usually have a date stamp near the hand guard cap, this one is 06/11.
The wick in the barrel extends past the chamber.
While a new in package M4A1 SOCOM barrel comes with a complete FSB (front sight post included), no muzzle device or slip ring/delta ring are included.
Colt M4A1 SOCOM barrels can be found for sale from various sources. These all are 14.5 inch barrels so it will need a permanently attached muzzle device to be legal on a non-NFA firearm. The Colt 6920 SOCOM model comes with a similar barrel that is 16 inches in length and does not have the M203 flats milled into it.