This is a simple demonstration of a Lyra camera conversion to fps view. Solution without changes in c ++ code, to be done in a few minutes. Not perfect, to be refined, but it is a good and working base.
As you can see, the bullets do not go in the direction of the gun, but in the center of the screen - that's what Lyra does, but can be easily tweaked.
The concept is to create a FPS FBA (Full Body Awareness) system with ADS (Aiming Down Sights).
If you want a tutorial - like and write in the comments.