For the last few decades a minor misalignment of the bolt on neck of my mid-70s Epiphone acoustic has annoyed me. But two of the screws were immovable and rounded out.   Today I bought a set of removal bits, but unfortunately the two screws sheared off... from the look of the two that unscrewed normally, they have rusted and expanded into the wood   I will have to try and drill them out. This might not succeed. I'm wondering if it might be better to make and use a core drill