How far away was the shot Phil? That is a lot of fish to turn fast.
To the OP, I think the noise definitely makes the fish move but the completely random nature of the movement is the X factor. I guess a quieter gun is better because it might be less alarming. I notice no differnce in fish behavior between my rob Allen and my wood gun. Wood gun is way quieter but the bands still make such a force I always figured the fish heard that more than the shaft on the track