A blank in an airsoft gun would be firing with nothing in it. Dry firing. Actually not that bad for the airsoft gun, some others would debate otherwise, but dry firing with an airsoft gun. A bunch of air pressure versus a plastic bb not even weighing a gram. It's like a mosquito hitting a truck on the highway, it won't make much of a difference.
Oro has a sniper rifle that can shoot a kitty litter box from 40 yds (.25bbs) Maybe it could've been better but someone broke it, and im not really sure if that affected performance.