What Brian has related here is EXACTLY what U.S.Customs have been telling me every time I check.This has been the case since mid 2005 all as per Brian's statement.
For parts coming NORTH the limit is $500 and CanadianCustoms are VERY decent so long as you do NOT try to "pull a fast one" and try to BS them about "go fast" parts.I have on a few occasions been asked to help I.D. internal parts for COMBLOC small arms which I am quite familiar with and probably will be again if needed.I do this STRICTLY on account of my NOT wanting to see the LEGITIMATE gun owners being tarred with the drug dealing,gangbanging,blowing each other away element,brush.In BC it is one particular group who seem to break these laws and could really care less if legitimate gun owners get hurt.