I'd say it had to do with it being real parts, I just got some stuff from HK yesterday (including a front end that included a fake low profile gas block); all opened and checked out by CBSA (you can tell what they looked at because they do a crappy job of repacking it, and the bubble wrapping is ripped when they pull off the tape).
Just because you're using it on airsoft, it's still a real part.
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