Check out Sci fi big gun for robot mecha Low-poly 3D model on CGTrader for $15. High-quality mesh by IzyaMoiseevich: 16149 polys, 17468 vertices. PBR, Textured, UV Mapped.
OBJ (OBJ, filesize: 1.93 MB), MAX (Autodesk 3ds Max, filesize: 139 MB), FBX (Autodesk FBX, filesize: 959 KB)