Agreed UPS policy is that ANYTHING (even parts and mags) airsoft related needs a firearms declaration form which is just a pain in the arse. The upside is that their tracking is pretty good and that the charges you need to pay are calculated accurately. Just beware of their drivers trying to pull a fast one and say that charges haven't been paid and asking for payment on the doorstep. Always have the receipt handy. its a laborious process but once you have gone via them a few time you work the quirks out.
although it does raise the question as to what various other companies are doing that prevent their parcels getting pulled by customs.....