Still looking for all of the information I can get, I finally thought of Mike Conner who, I have learned, is a font of good fly fishing advice. I asked for information on leaders specific to spey rods.
With his permission, I am including his entire response for your comment/experimentation. Here it is, I look forward to your comments:
I use long ( up to twenty five feet ) leaders with butts which are about 3/4
of the size of the line tip. I also use some furled leaders which match the
tip size exactly.
It really depends on how stiff the leader material is at the butt. If the
material you are using for the leader butt is a lot stiffer than the
fly-line, then you should reduce the diameter until it is about right. If
it is softer, then increase the diameter. The object of the exercise is to
get a smooth power transfer, and this will only occur if the leader and line
are about the same stiffness, more or less irrespective of diameter.
One way to test this is to connect a leader butt to the line tip with a
needle knot, and holding the line and leader in each hand about three inches
away from the knot, ( less for softer materials), simply bend the two
materials into a semi-circle, if the arc of the semi-circle is correct, ( a
circular arc !
), then the materials are well matched. If the knot
"hinges" or one side of the arc is out of shape, then the material is
unsuitable, or the wrong diameter. If the fly-line side is out of shape,
you need softer material, or lesser diameter, and if the butt side is out of
shape, then you need stiffer material or larger diameter.
Fly-lines vary considerably in their stiffness, and also in their tip
diameters, and so your only choice is to experiment until you find the right
butt material to suit your line. Normal nylon will usually work OK when it
is 2/3 diameter of the tip. Hard nylon will have to be less, and softer
Direct measurement with a micrometer is not a lot of use, as it is indeed
the stiffness which is important.
For very long leaders I have had great success with furled leader butts. You
can obtain instructions on making these here:
It is certainly worth the trouble. The leaders are much better, last a long
time, and may be custom built to your purposes. They are very much better
than braided leaders. You can also make them of a variety of materials for
Regards and tight lines!
"Where fishing is concerned, most anglers are basically manic excessives"