You won't get caught, carry the gun...
I transported 5 guns on the Subway and bus with my friend. We had a few duffle bags and just but some cheaper guns in bags and carried them. You won't get caught. The constables won't ask what you have in your bag. Just make sure the gun is covered. I don't have any legal standpoints on carrying Airsoft guns on trains or busses but you can do it no problem.