Making a lens

How would I make a gun have a lens for ttt? When I say lens, I mean like on the Aug for example, you could be looking through the lens, but all you would see is black. I want it to be like looking through the scope, but not fullscreen a full view.

Sorry if my grammar is bad, I’m not that good at describing things.

bump

Look at the code for the rifle I’d Imagine

But that is a fullscreen lens, I want a lens that would be from the view of the ironscope

3d2d textured rectangle maybe?