There appears to be no consensus on this site regarding wandless magic in HP universe. While answers to many questions (for example, "Are there any spells that a wizard/witch can cast without a wand in the Harry Potter universe?") convincingly argue for wandless magic (of wizards and witches, I mean), I also have responses from well reputed users that wandless magic is not supported by canon.
There are some magical acts which undeniably do not require a wand, like the Animagus transformation. The case of Apparation is again disputed here, but the scene in Half-Blood Prince where it is taught doesn't show the use of wands at all.
But the subject of this question is the possibility of duelling wandlessly. Specifically, can the Disarming Spell be cast wandlessely to expel a wand?
Some wizards are known to use objects other than wands to channel their magic, for instance Moody uses a staff in addition to his wand, according to Wikia. And Ollivander tells Harry in Deathly Hallows the following: “Oh yes, if you are any wizard at all you will be able to channel your magic through almost any instrument." (But again one reputed user has commented on this site that she takes it to mean only wands.)
The Harry Potter Wikia seems to give the impression that almost any magic can be performed wandlessely, given sufficient skill and practice. But there is at least one thing that leads to a slight inconsistency when it comes to Expelliarmus.
For, wands switch allegiance when their owners are disarmed even when they are just won, physically or magically)!
Won't the wand support its new master against the inherent magic channeled by its old master, given that it has also 'known' his magic, creating a situation analogous to Lucius's wand breaking in Voldemort's hands against Harry's, as explained by Dumbledore in 'King's Cross'?
Another confusion is, if A disarms B of B's wand and then B disarms A back wandlessely of A's wand, whom does B's wand now owe allegiance to?
The theory expounded in the books suggests the answer A, but now B can pick up his old wand and strike his enemy. Will it now still support A? This confusion remains even if A disarms back using other wands or staff etc., something that could have really happened with Moody using his staff.
Is there a way to settle this question, or resolve these confusions, as the case may be?
(I am not sure this a legitimate question at all for this site.)