Battle Rifle - Modeling practice

I've never tried doing a gun model before, so finally gave it a shot.
Personal project I've been working on for awhile with focus on modeling. I also tried my hand at optimizing it as a semi game ready asset with textures and normals baked down to a simplified model (See sketchfab viewer)

Inspired by the concept art of Eddie Mendoza https://www.artstation.com/artwork/Z5adbm