What is Reddit's opinion of5pc Carbide Burr Set 1/4" Shank Tungsten Double Cut Rotary Die Grinder Bits - Cutting Burrs for Milwaukee, Dewalt and Die Grinder Accessories - Wood Carving Metal Working & Sturdy Storage Case?
You can try drill the cap of the bolt off. Use a small diameter drill, to drill the center. Then you use n carbide file ( die grinder bit). The type they use in air tools.