In country airport to airport passenger service is not an issue, I've travelled with my Airsoft a ton.
1) ensure it is unloaded, mags kept separate.
2) remove the battery take it in your carry on, most airlines will not let you check the battery for fire reasons.
3) ensure it is in a lockable case
4) when checking it in ask for a declaration form, if they are unsure what form you need it is the same one they have you fill out for paintball guns.
5) they will send you and the case to security baggage for an inspection, be honest with them and do not try to hide anything (once again make sure it is unloaded and mags in a different bag)
6) guard will check it over probably ask a few questions with a big grin on his/her face
7) proceed to security yourself while your gun goes town the conveyor belt with your luggage
8) travel safe
9) pick up it and your luggage from the carousel at your destination
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