FYI, I just went to a Bluegrass tutorial weekend (Sorefingers) and the (excellent) bass guy, Ben Somers, slapped Spirocore mediums with no problem - but as AndyBass said he was not doing a triple rockabilly slaps, it was more your Folsom Prison type palm slapping for the most part and tastefully applied in small doses, rather than high octane slapping from start to finish