You need to let everyone know BEFORE you hand over luggage (not shouting, just needs to be said
) and take nothing in hand-luggage.
(I know that this is about magazines, that i wouldn't normally expect to be a cause for alarm)
I have travelled with quite large amounts of kit (m4 , 2 pistols, 8 mags for pistols and 12 for the M4 plus sundry kit) and the key for me was to alert the check-in that i have 'sporting equipment' that needs to be x-rayed by SECURITY (they'll just tell you it's fine but you need to INSIST that you need to go to the security check/desk)
usually it's the out-sized luggage check in (ski's etc)
go up to them, explain the situation, they'll x-ray and usually ask to be openned, they'll handle and be fine (if you're not trying to bring in a 249 in one piece) and mark it as 'security checked' and you'll have no problems.
just remember, NEVER use the word GUN or WEAPON. they may or may-not know what airsoft is, they will use the x-ray first, then looking at the working parts
GBB rifles owners, pukker that a-hole for a while, it could take a bit of talking and showing them the bolt (material, lack of locking lugs for the bolt, lack of gas parts et)
and magazine, to 'show' them that it's not real.
AEG owners can relax a bit, once they look into the magazine well and see the gear-box they tend to settle down.. open the dust cover (if you have one) and show them the lack of working parts.
bring bb's and be prepared to load them into the magazine (but NOT into the gun)
Vent any magazines, maybe keep the slightest amount, for the sake of o-rings, but be prepared to vent them (storage of pressurised gasses is another kettle of fish) if they want. (don't argue, you'll be happy that you had only a small amount in it now, otherwise you'll need to vent it somewhere safe)
Most of all, this only works in countries that allow airsoft, declaring that you have airsoft in a non-airsofting country = nasty (i imagine)
Be polite, be calm, be prepared to show them ANYTHING to make them feel happy.
this is how i avoid getting the rubber-glove treatment (working so far!)
ALSO: an unexpected benefit, because your luggage will be checked by security, it's possible to avoid paying for extra weight, just insist (nicely!) that you want it checked in by security. they'll hand you your boarding card without checking the weight and the security guy doesn't care about weight.