Hello Frank.

I posted quite a bit when I got my 16ga rolling block with straight rifling. The Swedish game law thing made sense because the bore was 16ga but the grooves took it upward of .690 groove. The gun seemed to be retroed.
Mic your barrel and it will let you know if you can use standard cases with a ball or thinner brass cases.

Cheers,

Tom

Carbonation without fermentation is tyranny