Any ammunition reloader with gunpowder can be turned into a pipe bomb/IED/WMD maker with a boilerplate BATF app.
Legal gunpowder, plus the crap anybody has in their basement, garage and workshop, plus one lie coerced out of a BATF snitch, and you too could be arrested as a bomb maker.
It takes even less than that, but certainly, that would suffice. Without going into details, it is trivially easy to make an IED without a chemical explosive charge.
which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant
That said (and I think the definition of WMD makes a mockery of the feds), if these clowns were preparing to assassinate local LEO, then they are in fact dangerous. Just like the cranky bootlegger is.