Dave- my .69 is the only gun that did not react adversly to the addition of a wad between powder and patched ball. For hunting purposes, where a rifle will be carried loaded all day or for days, I used a wad as a barrier between the two- but that rifle didn't care. Since my other guns do care, one must access the difference (if any) through actual testing and make your own decisions.
For an addition wad to improve accuracy, it must be incorrection of a problem, such as too loose a patched ball. Look to the round ball bench rerst shooters - are they using wads between patched ball and powder? If they are, then perhaps we should be as well. Wads are used in ctg. guns with soft bullets to ensure minimal damage to the base of the bullet, ie: to protect the bullet. Jacketed bullets don't need, nor use wads. In our round ball guns, I feel the patch is our jacket that is all the protection I need.
Now, if I want to use a barrier wad for hunting, I must access the damage it does, if any and see if I am comfortable in it's degree.
It would not hurt to try different wads materials - cardboard (or a dry patch), which I used in the 80's for moose hunting, worked just fine. Today, I'd probably use a 14 bore "B" wad from Track. Arch punches are about $20.00 at a hardware store - the material,an empty Cherrios box, is probably in your re-cycle bin.