Can You Work Out What This Thing Was Used For?

This thing looks like a cross between a gun, some weird cooking utensil, and an elaborate medical instrument. It is of course none of those things: but can your work out what it was used for?

Struggling? Well, it is in fact an eprouvette: an old-time device that was used to test the strength of gunpowder. Fill the device with 'powder, fire it, and the explosion in the barrel pushes the gauge out; the further it sweeps, the stronger the gun powder. [National Firearms Museum via Neatorama]

Image from the National Firearms Museum