I've made this a few years ago, But the textures and the GEO were lacking. So I decided to redo it, with proper low-poly geo. tris 12859 4k Texturesgame
Cool but the scratches look very procedural and they are continuous on different surfaces. In that last shot theres visible tiling in the metal material.
Scratches do look very procedural indeed, the materials themselves could be improved and defined better. Everything looks grungy and cloudy at the moment. Take a closer look at a actual Benelli M4 and a look at this small tutorial by Ben Bolton https://polycount.com/discussion/comment/2623619#Comment_2623619
The geometry does not reflect real world in most areas. It's an approximation but not accurate enough for close renders. I would list specifics but it's basically the whole thing.
If you have access to a gun store that has these it would be worthwhile to go there and ask if you can take reference photos. That way will be easy to make precise measurements.
If you are committed to rework the model and can't find good ref I can provide some for, have an m2.
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In that last shot theres visible tiling in the metal material.
I don't know if I'll re-work this model, but I'll keep in mind your pointers.