I have read before that Susato whistles had conical bores. I have always thought they were cylindrical, because they look cylindrical, and I have posted before that I believed they were cylindrical.
Which is why I am posting this. I was wrong.
In playing around with some wooden dowels and seeing what instruments would take what size dowel–a friend is building me an instrument stand–I discovered that on both the Susato small bore D and on the very small bore D models a dowel that will fit into one end of the body will not fit into the other.
The bore is, in fact, conical.
My apologies to anyone I may have previously told otherwise.
–James
During the early days of my serious research into whistle construction, I took measurements of all the whistles in my collection to try and better understand the relationship between bore diameter, window and windway dimensions, and tone hole sizes.
I was quite surprised when I discovered that Susatos had a slightly conical bore in spite of having a cylindrical exterior… pretty cool, eh? 
Is that why they’re consistently in tune?
Probably one of the factors, also Susato whistles have quite a bit of resistance and a fairly tight voicing, the conical bore may help a bit with that.
It’s conical but it’s not very conical: it’s a very subtle taper.
By the way, a fellow Chiffer was at a session with me not long ago and tried my plain-old Susato (not the VSB). She played along with a tune and stopped with her mouth open, looked at me, and said “But that’s nice!” 
I guess from reading the boards she was expecting a squeaky squawky nightmare of a whistle. :roll:
I really enjoy playing my Susatos now; I think they are good whistles. I do understand why folks don’t like to see a beginner with Susato in hand, though. They have volume and they will be heard.
–James