The Barrows has more of a sharp slope from the bill to the top of the head which is flatter than the Common.
Common--
http://www.pbase.com/tgrey/image/90324789
Barrows--
https://www.flickr.com/photos/soarin...n/photostream/
It is a close call but there is a slight difference. Your profile doesn't say where you are from or saw the bird. Barrows are normally found in the North Western areas of the US and near mountainous areas.