Daryl,
Groove diameter is .729", have not measured bore diameter, it's a 7 groove barrel, which measuring bore diameter of an "odd grooved" barrel is above my limited mathematics ability!
Might have to push one of the round balls through and see what I can measure.
Twist is 1 ~ 20", fast for a 12 bore, but it likes the round ball loads, which I might say I loaded after reading your posts quite a while ago.

I am convinced I can be competitive with round balls at the 25 and 50 metre ranges, at 100 metres, the Paradox style projectiles come into their own.

Thanks to everyone else for the comments.

Neale, got a new mould coming for it, 900 grains, you can be the first to shoot them if you wish!

Here's a picture of it, mould should be about 2-3 weeks away.

Regards,
David.