Hello There,
I briefly owned a Chieftain High D, didn’t care for it, shockingly loud and took a huge amount of air to reach the top end of the second octave. However this whistle did have two features I liked (and I’ve been unable to find with any other whistle) a much larger bore, and much larger holes than a ‘regular’ High D.
Does any other High D have a similar bore and hole size, but has a friendlier volume and air requirement?
There’s a direct relation between large holes, a large bore, a high air requirement and volume.
I thought that would be the case (I almost asked that in my post) shame 
Perhaps you are still asking the wrong question. If all you are looking for is a larger bore tube, that still sounds softer or has a more moderate volume, a whistle made out of a thicker material may suit you well (i.e. a plastic or wooden whistle). The one I made out of 1/2" CPVC with a wooden fipple, loosely following Dr. GG’s plans, is by no means strident, but does feel like it has a larger bore than the typical Generation/Sindt/Feadog high d tube. Unless you want to relocate the toneholes a bit you will still end up with more standard openings there. Kind of unusual to be asking for larger diameter tone holes, most players I’ve spoken to seem to prefer them to be as small as possible to make ornamentation easier (though I guess if you do a lot of half-holing, that could be a good reason).
Also, though I’m certainly not close to being as experienced as Mr. Gumby at this, I believe that the fipple configuration has a lot to do with the air requirement and volume of a whistle. In fact the Freeman Mellow Dog high d whistle uses a “c” whistle diameter tube and fipple which is appreciably larger than a typical high d, but is not exceptionally loud or needing a lot of air (though those are subjective characteristics and YMMV). OF course the toneholes on the Mellow dog aren’t particularly large either.
Not to be argumentative or anything but that does not have to be gospel.
There are a lot of larger bore high D whistles. These do not necessarily follow the same design dictums in the mouthpiece, or anywhere else for that matter. You can find free blowing whistles, which may have a higher air air requirement, and there are less free blowing models, which should use less air. But some whistles are just more efficient than others. Some free blowing whistles speak quickly and easily across the range while others might not.
There have been several generations of Chieftain whistles over the last 25 years or so. Not sure which type you may have owned. The old style Chieftains I owned/played in the late 90’s were not free blowing, IMO. They had a narrow-ish windway height and it took some effort to build enough air velocity to generate the high notes. They were large bore, large hole designs. But they did not use a lot of air. In fact they used less air than many other whistles I owned at that time. But yes, I had to blow hard to get to the high B, but it was quite predictable in that regard. The narrow windway has some advantages which can make it quite likable.
A large bore whistle with large holes that has a smallish voicing window might actually be a quiet whistle.
A whistle is a composition of many variables. Buy 'em all. If you still have not found one you like, make your own. 
Feadoggie
Perhaps my description was awry, I was regarding ‘a lot of air/blow hard’ as synonymous but from your comments above I take it they’re not (volume/velocity etc) ?
PS: My Chieftain was stamped 2012.
Sorry I thought I had said that?
I do very little ‘half holing’ actually (in time perhaps?) the larger tube felt more comfortable to hold, my hands didn’t get as tired as quickly as they do with a small bore, I felt I could player faster, with greater fluency (given my limited ability) and the larger holes seemed to improve my slides, bends, vibrato etc.
Does any other High D have a similar bore and hole size, but has a friendlier volume and air requirement?
A larger a-hole is usually louder, and the “air” required isn’t very friendly either. It should be stated though: this has nothing to do with tin whistles, but it could be anecdotal.
Everything is relative. Yes, there are a lot of whistles that have a similar bore and hole size and a friendlier volume and air requirement. But it is all relative.
I could list maker after maker and once you got hold of those they might not suit your “friendly” requirements. It’s all relative.
Bore size and external diameter can vary depending on the tube material. A 1/2" bore whistle made of wood or heavy gauge aluminum will have a larger external diameter than a whistle with a thin wall aluminum or brass tube. It’s all realative.
A thick walled tube might have smaller tone hole openings but be well undercut internally so that they are, from a physics perspective, just as large a hole as on a Chieftain. Relative?
One whistle that comes to mind when you post these requests is one of David Boisvert’s Greenwood whistles. They are large bodied whistles. They do have a large bore (relative to what?). But they are fairly demur and well behaved whistles. I like them a lot. i sold mine because I did not think it was loud enough for my needs at the time. But it is all relative.
David O’Brien makes nice whistles. They have a bore and holes. They are nicely balanced and not overly loud. But it is all relative.
John Sindt makes excellent whistles, They are thin walled so while the bore is generous the whistle does not feel so large in the hands. The volume is moderate but good, IMO. Still, it is all relative.
Mack Hoover makes really fun, quiet whistles. But it is all relative.
I could go on.
Try 'em all. Buy 'em all. Keep what YOU like.
And remember, any whistle can be played quietly.
Feadoggie
“David O’Brien makes nice whistles. They have a bore and holes.”
I should hope so!
Cheesewhiz! You had to catch that, didn’t you? 
Hi, David.
Well, they do have a bore and holes. Right? Not to large, not too small. Just right. Goldilocks plays one, or so I’ve heard.
Feadoggie
It’s all relative 
I have just invented the bore-less whistle. A radical concept where, turning conventional design on its head to defy the laws of physics, the whistle is turned inside-out so that what used to be the bore is now on the outside and therefore infinite. With no further need for holes since it’s not going to work anyway, the non-holes can be as big or as small as you like (you could even stick your head up through one from the now non-bore inside playing position to inspect the now infinite ex-bore outside), but rest assured that at least blowing still makes a sound unless you blow too gently to hear…
Oh, and of course it’s musically immune to turbulence with no round, square or hexagonal cross-section to pose design problems!
Latticino wrote:
Perhaps you are still asking the wrong question. If all you are looking for is a larger bore tube, that still sounds softer or has a more moderate volume
Sorry I thought I had said that?
ThomasNashJohnson wrote:
Does any other High D have a similar bore and hole size (RE: Chieftain), but has a friendlier volume and air requirement
Sorry, guess I wasn’t clear enough in my post and actually made the same semantic mistake. As far as I know the bore of the whistle is the inner diameter of the tube used. You seem to be more interested in the external diameter as regards the feel of the whistle in hand. Here my, and others, suggestion of a whistle with a thicker tube wall makes more sense.
Based on the further details you have given I reiterate my suggestion of a CPVC (like the Parks), wooden (Sweet or Busman) or Freeman Mellow Dog. These all have larger than “standard” Generation high d tube outer diameters and can be played at user friendly volumes.
Also completely agree with the other folks posting, “it is all relative”.
Just when I thought everything had been stated and done… another whistle… WHOADY, WHOADY, WHOADY!
No.
Thank you, and no apology needed I assure you. Parks is an interesting suggestion (I suspect the Sweet and Busman are beyond my budget) and a Freeman (in fact a number of Freeman’s) is already on my ‘to buy’ list.
No what? No, I haven’t invented it or no, you don’t want one?
perhaps take a look at susato whistles, and pretty much any wooden whistle (dependant on budget of course), parks was also a good shout. Will feel like more than just a thin brass tube in your hands, which seems to be what you’re looking for.
The Shearwater session/big bore high D has a lot less volume than the Chieftain big bore high D.