and since firing may be minutes away
I've never run into a problem where it would "take minutes" to fire a BP to clear the range. It doesn't take any longer to fire than any other single action weapon--where did THAT come from?
You should not be loading if people are heading downrange.
Finish the chamber you're futzing with and fire. Or, place the cylinder open end down on the bench. Or, stand the rifle upright. Or, fire it off.
If it's pointed downrange with something in it, it's loaded. If you imagine otherwise, you're wrong. Snap cap, magnum load, BP...doesn't matter. Don't point it downrange.
AR guy should have just started laying out gear, adjusting, loading mags, setting up scope, and waited for BP guy to figure it out.
If BP guy feels a need to make a point enough that he'll refuse to shoot in a timely fashion or point his weapon in a safe direction, because he WANTS people to walk downrange while he's got a loaded chamber, have him politely escorted off the range and tell him not to come back.
But don't argue over it.