Theoben prometheus may be one.
Designed for using Prometheus pellets. Unchoked barrel.
From another forum.
The Prometheus is a Scirocco Classic with unchoked barrel purposely made for use with Prometheus Paragon pellets. I've heard the rifling in the barrel is different but can't confirm this. The twist certainly looks different looking through the barrel.
If you're unfamiliar with Paragon pellets they were sold in self-assembly packs. Plastic bodies with zinc heads you'd ruin your thumbs pushing together 500 at a time. Tended to leaves strands of plastic in the barrel.
The barrel is stamped UC for unchoked.
From Trev's scrapbook.
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