Die Ökonomie-Musterbücher was the purchasing specification for the Habsburg/Austrian army. Anything the army wanted to purchase and have it paid for by the government had to come out these books.
There has been little research on this angle of inquiry regarding the Girandoni but I do have one report that the Girandoni itself does not have a specification but the accessories do. What's available on the internet is limited but there is Specification 5023. It details the Windbüchen - Flaschen- Futteral sammt Trag - ind Flintenriemen or Airgun-Airtank-Case, together with carrying strap - and gun belt (sling). http://books.google.com/books?id=T8N...üchsen&f=false
What's nice about the Militär-Ökonomie specifications is that there is no question that this item really is for an original Austrian miliarty air gun. No opinions, no assumptions, no questions... other than, there is no assurance that this case and sling specification is for the Girandoni. There is evidence that there were other less distinguished air guns used by the Austrian military, particular the Grenzer troops. The dates on this spec are 1798 and 1803 (? on the 3) which seems a bit late to be for the Girandoni.
We've all seen this knapsack that reportedly was for the Girandoni.https://en.wikipedia.org/wiki/Girand...rments_Bag.jpg
If it comes close to S.5023, I have no idea, but, at least, there is now an official specification for comparison.