Sentry Gun Low-poly 3D model is available on CGTrader for $12. Original author: edplus. Specs: 4374 polys, 2311 verts.
STL (Stereolithography, filesize: 64.8 KB), OBJ (OBJ, filesize: 58.1 KB), DAE (Collada, filesize: 136 KB), FBX (Autodesk FBX, filesize: 96.9 KB)