Check out Trijicon ACOG4X32 Low-poly 3D model on CGTrader for $60. High-quality mesh by SilentSymmetry: 24777 polys, 12962 vertices. PBR, Textured, UV Mapped.
BLEND (Blender, filesize: 99.3 MB), OBJ (OBJ, filesize: 2.22 MB), FBX (Autodesk FBX, filesize: 109 MB), PNG (PNG, filesize: 171 MB)