Sounds lke you have been doing your research, many Air rifle loonies shortent their barrels. I never have.....but did have a full stock underlever cocking BSA Stutzen once in .22 cal. They had 14" barrels. It was not particular fast, it was a demo model, took me a year to get it after seeing it at a SHOT Show. Not many made, kick myself for selling it. Mainspring was broke in two likely from dry firing as a Demo. It was like new in box, but I was lucky to get a new Mainspring and the velocity went up.
It was harsh firing, Accuracy with Eley Wasps was fantastic, that and RWS Domes and Super Points were it's mainstay.......British bores tend to run on the large size and my former BSA Meteor .177 liked Benjamin roundnose, but I settled on RWS Superpoint in the mild powered springer.
A bit of trivia for folks who might not have heard of these rarities.
https://www.gunstar.co.uk/community/reviews/airguns-reviews/bsa-s-airsporter-stutzen
