In the past I've always put a felt wad between the powder and the ball mainly cause I have them on hand and want to use up my old batch. I still have several hundred wads left over from a felt hat that I cut up. But is this step really necessary? It's kind of a filler since I use light loads of powder.
When using light loads in a revolver, is it really necessary to use a filler, be it a felt wad, cream of wheat, corn meal or grits?
There are any number of factors that enter into an answer to the necessity of an over powder wad.
First is what are your expectations and desired results when you are shooting your revolver. Top shooters looking for the most accuracy seem to have the best results with a balanced load of a highly accurate powder charge, bullet configuration, and a stack of wads or filler that positions the bullet just below the surface of the chamber mouth. Having the shortest distance to the beginning of the rifling seems to result in the best accuracy on target. The fillers and wads take up space so that there is no gap between powder and bullet.
Second is to account for the manufacturing methos of drilling the chamber in the cylinder. Some of the drilling and finishing results in a slightly tapered cylinder. As the bullet is pressed deeper into the cylinder, the diameter decreases. As the ball is fired, the ball must expand more to fill the grooves in the barrel. The fillers and wads ensure that the ball is at the largest diameter when the ball is fired to take advantage of the obturation of the ball to expand into the grooves and follow the twist of the rifling.
Third is a belief that having a lubricated wad will keep the fouling soft, minimize gas blow by and perhaps block hot gas from an adjacent chamber from causing a chain fire. This is secondary of course to using a properly fitting ball that shaves a ring of lead off the ball to seal the chamber.
Fourth is that the wad is not necessary if simply shooting for plinking accuracy and the ball or bullet makes a good seal. Then one has to take care to have properly fitting caps on the nipples.
A long reply to the question and providing an answer that is simply, "It depends".
No harm is done if using the wad.
