Appreciate you seeing my viewpoint.
I had originally thought about using the custom depth/stencils to create my mask for the lens, then using that to mask the gun, exactly as you said. I looked at videos of COD and slowed them down frame by frame and you can clearly see the gun is masked out real time through the lens where it should be visible. And obviously I knew that some games render FP seperately to do this sort of thing. Its a real shame an engine as good as UE cant do this, and I fail to understand why they wouldnt be interested in making it work by default.
Do you know of any games/projects that have gone to the lengths of making engine changes to make it work? How much effort is this for someone experienced in that sort of field, do you know?
And yes hopefully we can come up with the next best solution that works in Unreal Engine for others to learn from and use to achieve similarly AAA results…