Thanks everyone, for the explanations.
I don’t think the whistles are ugly by any means, it’s just that the bulge makes them look a bit “techno.” I like my Sindt because it’s quiet, simple, and unobtrusive, in terms of both tone and appearance. But I’ll probably buy one of these narrow-bore brass Burkes anyway…two friends of mine have bought them recently and they’re both raving about them.
Due to aforementioned bulge, the Al-Pro I used to have was referred to as “the Sputnik” at a session I used to attend.
Hi Everyone,
I just got a private message pointing me to this thread. Just a couple of comments on the O’ring and the bulge and the expansion.
You are all correct. 
The Bulge is there as Bretton and Raindog said, to house the O’ring that makes the slide smooth and completely airtight and to make it last for as long as you can imagine, since the O’rings can be replaced if you ever wear it out and it is brand new again. The O’rings have 1/16" thick sides on them, so the OD of the O’ring is somewhat bigger than the ID. This produces the
“Bulge” that everyone notices in the slide. I made the "Bulge’ to have facets on it in the way that a jeweler facets a stone or gold to make it sparkle. It is a case of form following function, and I like it personally, but not everyone does. I have modified the slides on my latest narrow bore aluminum whistles
to have a larger flat in the middle and make it look less abruptly “bulgy” if you will. I like to make everyone happy, so I may do the same with the brass at some point, even though I like them, as I said, like they are because they sparkle in the light.
There is also a pert near this point as well, so the people that thought it was there are right too.
Thanks for all the kind remarks. I am always around and am paying attention to you, my great customers so we can give you the whistles you need to make beautiful music. I had been away for a couple of days and missed this thread, so thanks for the heads up message as well.
Happy New Year and All the best
Mike
Amen as to the Burke Narrow Bore whistle. As I have said before, they will have to pry it from my cold, dead, fingers before I will part with mine!
Tres
Amen as to the Burke Narrow Bore whistle. As I have said before, they will have to pry it from my cold, dead, fingers before I will part with mine!
Tres
Amen as to the Burke Narrow Bore whistle. As I have said before, they will have to pry it from my cold, dead, fingers before I will part with mine!
Tres
Say it three times, brother! 
Amen as to the Burke Narrow Bore whistle. As I have said before, they will have to pry it from my cold, dead, fingers before I will part with mine!
Tres
OK, four is good too!