I don't think I can provide a "smooth" 0-1 based on the animation.
It would be a hard flip. Which brings the question, does it flip at the start or end of that animation, and would that be annoying?
"isGunnerView" as name? You do mean "is zoomed in" but.. yeah.
But, what do you want to use that for, would that not cause visual issues?
Your one animation source, would be applied to every weapon, also the weapons of other units that you see infront of you.