On the topic of importing upgraded guns, there was a thread in the AoM discussion forum (link here if you're AVed: http://www.airsoftcanada.com/showthread.php?t=145051
) where this was said:
Originally Posted by COL.TIKER
I'm not sure if that [importing upgraded guns] actually works. I was told via phone by a CBSA agent that they only go by the FPS they find in physical or online manuals for the gun, not whatever the retailer claims the FPS to be. I asked if they can chrono the gun to verify that it is over 366FPS instead of whatever the manual says, and his reply was "sure, if you want it to wait in a line up for the next 2 years"