I wrote out a very long post, but I’ll just condense things a bit by saying, I got the brass narrow bore C, and I really like it!
Due to not having a session bore C, I can’t compare air requirements or responsiveness, but I can say that the narrow bore C has , as far as I can tell, identical air requirements and responsiveness as my session bore D.
That’s not all that is identical, either! Holding the session D and narrow bore C side-by-side, I noticed that most all of the parts are identical in dimensions and appearance, exactly. It appears to be a session D with a longer tube! I am sure that many fine adjustments are made that are not visible to the eye, which would differ it, however.
I own burkes above and below this key, in either the session or standard bore size for those keys. So, I think I can spot some differences between this burke and the others, though as Feadoggie said, the differences are slight.
The lowest notes have a bit different of a sound quality, compared to the keys a bit higher and lower, and not narrow bore. Can’t speak of it one way or another, it simply sounds a bit less “Ooooooo”.
The highest notes of the second octave, which are usually more piercing than other notes of that octave, have a much less piercing quality in volume. Yet the other second octave notes on the whistle sound as you’d expect. This is a big thing I enjoy about this whistle. The consistency between volume of both octaves is great. Neither octave is quiet, but the super high notes (Second octave B, and c, [octave above c natural] ) are a bit quieter, so that they are a closer volume to the other notes. On many whistles I find these notes are a bit louder than I’d prefer, and cause a big spike in volume when I come to them in a tune (which in some cases can be desirable, but in most tunes I prefer them balanced, as they are with this whistle).
That also leads to something I expected in this whistle, which also relates to consistency- The pressure required for notes. What I just said about volume in those higher notes, applies to pressure, too. I don’t notice a big spike in the amount of pressure needed for the very high notes. The second octave uses very similar pressure throughout the entire second octave. It is not in such a way where there is a big increase in the amount of pressure needed for a second octave B, over what might be needed for another second octave note below it. The conistency in pressure makes this a whistle that is very easy to get a natural feel for the pressures needed, even after about the first minute of playing it.
It’s a very easy player, the volume is great throughout, though toned down a slight bit where I think it needs to be, and the pressure required for all the second octave notes is more consistent throughout, with the higher notes not needing a great deal more pressure than the notes a bit below it. I think the things relating to volume and pressure are likely the primary differences. Though, also as mentioned, all the other burkes I’ve played do really well in these areas, too. I just notice even more of a difference on this narrow bore, than I do on all the other burkes I own in surrounding keys.
I think the bit of differences I can note all relate to the various qualities of both extremes in the high-low spectrum. Pressure and volume is better in the very high notes, and tone is a tad different in the very low notes, slightly. Volume in all notes is excellent, and the low notes are by no means weak. I think this sums it all up, pretty much. It’s a good whistle, and I’d recommend it.
I do wonder though, if the narrow bore D has the same size head and parts as the Eb whistle,as this does with session D, but that’s a different topic.
Good luck choosing the right C whistle, but either one would be good. I think this one is probably a bit easier to play, but the other burkes are not difficult players either. It juwst depends on what you want in a whistle. I also recommend getting both and keeping the one you like. That is really the best advice that was given in this thread, and will guarantee you get the right one for what you are looking for!
Edit- I am terrible at condensing things.