I have been finding (once I became comfortable with the mechanics) that the ABA triplet has started to supplant good-old-reliable ACA. To my ears, the C in the ACA can sound unmusical in many tunes whereas the B in the ABA is much less jarring.
So why has the ACA become the default triplet? I find it ironic that many pipers will eschew a back D cut for its harshness, but are quite at home with the ACA triplet.
The ACA triplet is the pneumatic drill of piping to me. Dreadful business.
I find the ACB a smoother alternative. A little easier on the fingers and ears.
Tommy
Awww, no! I’ve been working so hard on those ACA triplets!
Or maybe I should be happy?
Apart from the C# being easier to play (arguable, maybe it’s just my dumb middle finger?), I’d say that AC#A sounds better (and it tends to be ACA indeed, as the C# does not go up to C# when this short, at least on my chanter) - and A and C go together well in harmony. On the other hand, A and B sound pretty bad (especially since the B is flat when played with one finger off, going basically down to B flat).
Of course, a triplet is not the same as a chord, but it is an approximation…
A B-C#-A triplet, where the B is played by opening just the second finger of the top hand, can be very useful. Séamus Ennis used it, for example, in the first bar of The Bucks of Oranmore, just after the A quaver or eighth note that opens that bar. This allowed the playing of a tight triplet in a crisp, relatively simple manner, whereas following that A eighth note with an A-C#-A triplet would make for a rather awkward shower of fingers, and perhaps a bit of that pneumatic drill of which Tommy Martin writes. In addition, the B-C#-A makes a nice tight alternative to a roll on A in reels, in particular… For example, try it in the first bar of The Silver Spear, for example, or the first bar of The New Policeman… Less jarring, perhaps easier to finger…
I’m fairly certain Ennis did not play that triplet tight. The only real staccato note in it should be the C#. The B from the A is a legato movement. It’s how he even wrote the tune out in his own hand. (It’s kind of amazing how detailed some of his transcriptions could be)
I am used to the ACA method. Gotta work on my ABC’s (hehehe punny) CBA’s and BCA’s and ABA’s abit though!
I have at least five separate recording of Séamus Ennis playing the Bucks of Oranmore, chaos97, and in each one he plays a B-C#-A triplet in a ‘tight’ manner at multiple points in the first part of the tune over several iterations. The movement from B to C# is not a purely legato one as you suggest; there is an infinitesimal silence between those notes, achieved, as I said, by fingering the B with one finger only. I am familiar with his transcription of the tune, where there is an indication of staccato on the C#. As multiple recordings show, in practice, when he used this triplet, it is a ‘tight’ one, as Pat Mitchell’s detailed transcription of Ennis’ actual playing of the tune indicates.
Got to get out of this desert and spend more time with you advanced piping types - neither ACB nor BC#A ever occurred to me, can’t wait to try them out. Up to now I’ve been a profligate hoor with those AC#A triplets, never realized why the others were always whispering and pointing 
Next you’re gonna tell me that The Kesh has been done to death??
I had a look at Pat Mitchell’s book and I don’t see the staccato B you are mentioning besides in the tune ‘outline’. Throughout the actual transcription the B’s are only marked by a comma after them, indicating a pause before the C. Also on page xxxiv he makes reference to this exact passage and says, “his use of a short upbeat A note before the bar, linked to the first B by a slur, should be noted.” & on xxxv, “even though all the note transistions other than from C to A are legato, the ear interpretes the ‘triplet’ as staccato-ish.”
Jimmy O’BrienMoran also mentions this triplet in his interview during the Piper’s Choice DVD and in his article “as tight as a…” Published in “the Piper’s Review” where he describes it as “staccato light” or something similar.
Regardless though, I don’t really consider it an easy substitute for the ACA triplet as the Ennis one is primarily used in the space of a dotted crotchet or a long roll, instead of the crotchet space the ACA takes up. I use it more as a way to avoid A.ACA movements as they tend to come out sounding clumsy or sloppy or stuttered for me.
Right there with you, my friend! xx
SO ashamed.
Don’t forget the GF#A backstitch!!!
I use it more than I should, but combined with the ACA makes bubbly magic! 
Backstitch. Yes, I think that is the key to the whole thing.
I think of the A.C#.A triplet as an isolated fossil of a more systematic approach to “ornamentation” that included backstitching, double-cut rolls, and “off-the-knee backstitching” that all employed the C# and A as the cutting or popping fingers on the left hand, and the G and F# as the cutting or popping fingers on the right hand.
Why C# and A? Because they are single finger notes, as are G and F#.
Remember, if you are backstitching notes played with the right hand, you use C# and A.
Remember, if you are backstitching notes played with the left hand, you use F# and G.
So, if you are used to backstitching with C# and A, it doesn’t surprise me that if you wanted to come up with a staccato triplet to replace a short roll on the A, you would come up with something that you already use.
The fact that they are single finger notes makes playing them staccato a little easier (remember how hard it was to learn a B.C#.B triplet because B took two fingers?), and it also makes them available as cuts: all of Chris Langan’s double-cut closed rolls used C# and A, and (if I remember correctly) so did Joe Shannon’s.
So I’m not sure whether it is right to attribute these moves to particular players or schools of piping (Tuohey et al; Henrietta Street ; Ennis), or just to see them as almost inevitable given the way we finger certain notes on the chanter. By way of example (or counter-example): Ennis did not use backstitching, but try backstitching a lower octave A: A (G.F#.) A. Ok, now, once you have that perfect, play that backstitch Off the Knee! And what do you get? You get the famous Ennis Instant Cran!
Thoughts anyone?