Yeah, I think it is. It's called a two-sided face. But how do you plan on having the zoom? If it's not a scope, and just a site, you could just move the gun in front and maybe also use a 2D sprite that appears the moment the gun in position that looks almost like the gun but a bit blurred.
You could also just create a sprite with a huge hole in the center (with all the appropriate markings) and place that on the screen when the user looks through the scope. You would animate, of course, the gun moving to the eye position, but after that switch to that image. I've definitely seen this done a lot in games.
I guess you could make your scope and physically move the camera to look through it, but I don't think it would work very well, especially after zooming.
So I wouldn't build the inside of the scope. I would create a slight bubble on both sides of the scope where the glass would be, and then put a shader on that part so it would reflect an HDRI image version of your level.
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