Here is a game-ready M60 machine gun, with PBR textures included in the files. This has 16696 polys (29654 tris) and 16229 vertices.

Materials in this asset are divided for the following:

Barrel Muzzle Bullet Bipod Main Rifle Magazine Pouch Hand Guard Sight

Maps included in this asset are the Base Color, Normals (OpenGL and DirectX), Metallic, Roughness and Ambient Occlusion.

As an added bonus, the World Space Normals, Curvature, Basic Normals, Position, Thickness Maps and the Color ID have been added for any re-texturing, along with a UnityPackage file.

This asset was rendered in Marmoset Toolbag 3.