It has been so good to finally meet a third fellowman interested in the same stuff!
The haquebut you referred to, illustrated by a line drawing in Essenwein's basic work, is still preserved and on display in the Germanisches Nationalmuseum Nürnberg.
I'm attaching the pictures I have taken over two decades, plus a b/w photo taken by the museum about 100 years ago.
The piece is about 1.60 m long overall, the barrel length being ca. 1 m. The snap tinder-lock nailed to the stock at the right hand side of the breech may be contemporary. The stock is oak, painted black. The complete piece might weigh about 20 kg (German: doppelter Doppelhaken
) and can be dated closely to ca. 1515-20. It was doubtlessly cast and stocked in Nuremberg.
The second piece on the images is dated 1534 on the bronze barrel, the present backsight being a Thirty Years War alteration (the original integral backsight at the base of the barrel removed).
In order to judge your haquebut, as well as the inscription, I would need to see overall images and close-ups.