ha, no wilson I didn't think you was shooting me down I just thought that I didn't explain it well enough which is why I said that I can understand why you might think that, and then went on to explain it more. truth is your assumptions were valid just turns out that wasn't the case here
mac the wire isn't tied to anything to induce stretch but it is being held snugly in the 2 cutting jaws and the winding of the coil is pulling against this restriction, inducing tension and strain. here's a quick sketch to show what I mean
now there is tension between the coil and the jaws and there are 2 points of mandrel forming that stress the wire into it's new form
the first bit of mandrel forming uses the wire itself as a mandrel, the approach angle causes this bit of stress which causes adhesion or compression. ever take a straight wire and pinch it between your finger tip and a tool and pinch tightly and draw the wire through this pinch? what happens? the wire winds up forming a big curve, it's no longer straight because one side of the wire winds up getting stressed more than the other, this is what happens at the first point of deflection at this approach angle meeting a slight change in direction, this forms compression or adhesion... what this does is not only stack the wraps but it makes them want to naturally pull into each other the way drawing a straight wire through your finger pinched to a tool causes the wire to curve
the second bit of mandrel forming happens right after the first but on a different plane and that's the one that turns a straight wire into a coil. in the pic I drew the bottom shows the first bit of stress forming while the top shows the second forming which is actually forming the straight wire into a coil
as far as using this for twisted wire I think that the twisted may be much harder on the leather, almost like a saw tooth action, forget about twisted ribbon like MM, that'll shred the leather to bits I think, the reason why the leather works so well is because it causes friction which increases the tension but it doesn't get damaged because the wire drawn over it is so smooth, start introducing jagged bumps of twisted and all bets are off, light gauge twisted prolly be ok, like twisted 32, twisted 30, but heavier I'm thinking will probably cause the leather to deteriorate rapidly. I haven't tried any twisted with this