Check out 20mm Anti-Aircraft Gun 3D model on CGTrader for $23. High-quality Polygon mesh mesh by 3DKAD: 137066 polys, 139466 vertices. Rigged.
BLEND (Blender, filesize: 1.32 MB), OBJ (OBJ, filesize: 3.74 MB), FBX (Autodesk FBX, filesize: 4.52 MB), STL (Stereolithography, filesize: 5.53 MB)