An impact-release system that ejects uncrushable material and then re-latches for non-stop grinding. A deflector grate and a chain curtain downstream of the grinding chamber redirect and absorb the energy of the ejected contaminated material. The adjustable release system can be set to suit the specific grinding job, releasing only when appropriate. A pinned rotor is available with this option for quick hammer replacement, as are heavy-duty grates and grate supports. Particularly suited to processing railroad ties and MSW.