"Sporting use" has nothing to do with the Right to Keep and Bear Arms.
RKBA isn't about "sports", or even about stopping street criminals, although those activities are protected.
RKBA is about killing tyrants.
Outlawing bump stocks could be seen as a safety measure. I could be wrong, and welcome correction, but as far as I know, it’s just an adolescent Rambo fantasy device, unworthy of real marksmen.