I brought some shells back with me when I was to Texas over Christmas and New Years. I ordered from Airsoft GI and had them shipped to my relatives. I presented my receipt at the border amongst all my other receipts for items purchased (wii controllers, DVDs, household, some clothing, etc.) Now this got the attention of the CBSA agent. His first question "You don't have any guns, do you?" I explained that I of course did not. He was familiar enough with AirSoft to get what I went on to explain. He asked to see the shells. I showed him said shells and explained how they worked, what they were powered by, and at what velocity they would expel BBs.
I was honest and up front, and it paid off. YMMV. Having a mailed parcel examined is entirely different as you are not there to explain. All my other M203 purchases, including launcher have been from airsoftparts.ca
Call sign: Usurper