Abstract: A composite drill collar for drilling bore holes in earth formations including a structural steel outer jacket having a lower end secured to a lower coupling connectable to a drill bit and an upper end secured to an upper coupling connectable to an adjacent drill collar thereabove. An annular heavy metal core of sintered tungsten is disposed in the jacket and is held in compression therein by preloading the lower and upper couplings against the ends of the core, which places the jacket in tension, causing the jacket to contract and grip the periphery of the core. The structural steel jacket has a thick wall to carry the bending, torsion, compression, tension and impact loads encountered in the drilling operation, so that such loads are not carried through the core, which has the purpose of increasing the overall density and mass of the composite drill collar, lessening considerably the tendency for a deviated well bore to be produced.