Ben - althought sometimes a slug mould was 'thrown in' with a cased double, or sometimes the reverse and a round ball mould was 'thrown in' with a slug shooting double. BUT - a gun is rifled for one or the other, not both. It will only shoot one well. Round balls are perhaps the easiest to set to shoot in a too-fast twist, but a slug becomes unwieldly in a slow twist, losing stability upon impact and not penetrating in a straight line - useless.

There was a time in the UK when gun makers were all wound up on fast twists for round ball guns. I'm speaking of muzzleloaders in the mid 1800's. Some went as far as 36" of twist and the guns were useless for killing game. Weound, they would do and well, as they would not take a proper charge to get the job done with one ball.

Ctg's and breech loading changed a lot of that - easier & faster loading & the makers finaly secummed to the slow twists for round balls and faster twists for slugs.

About the slowest twist useable for a .73" slug would be around 60" with the slug being short like the collar-button or Paradox-type.