That's pretty cool, an adjustable powder measure as well. Not sure what the 2 different sized rectangular holes are for, appears could be a wheellock spanner, but I doubt any maker of those
also included an ADJUSTABLE measure with it. Normally, measures included with guns were for a 'fixed' charge, were they not?
They do not include a picture of the end, with the tube pulled out, but the one picture of the top end, shows a screw into the end of the non-moving part with the stop holes. This will be the base
of the adjustable tube to stop the powder. This is similar to most all modern adjustable powder measures.
It ides have an antique appearance, but then, there are lots of fakes, "out there".