Just need a locked gun case and declare it as "special baggage" (eg. Snowboard, hunting rifles, oversized baggage etc.)
Just a warning though. I've head that Airport Security loves you to take out your rifle so everyone can pretty much see it (you need to prove nothing chambered, ammo seperated, etc.).
It should be fine though. All they care about is that it follows all air transportation rules. If it's airsoft or real steel it doesn't matter to them. I also believe there was some sort of form you have to sign just declaring that you know everything and that all ammo is separated and nothing chambered. There was a picture of this form floating around somewhere on this site (it was an Air Canada form).
One more thing. Keep the locks on the case but unlocked when they go through security. I believe they need to check it as it passes through to the secured side of the airport and if the break your locks then..... yeah.... They should be smart enough to lock your case after checking it. If they lose your package don't give hell to the front line guys it's the rampys (AKA ramp rats) fault that your shit was damaged/lost.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE