Some folks use grease cookies, wads of stiff semi solid lubricant under the bullet. Some folks seperate the gease cookie from the powder and bullet with card wads. I myself load 60 grains and a grease cookie and a 500 grain bullet. In a trapdoor it will still bruise ya and is not by any stretch a reduced load.
Some of the very old lyman catelogues and instructions for "sqib" loads. Even to shoot round balls.
Cotton was used in olden days as was carded wool and kapok. I don't like fillers and try to avoid them. 45 caliber punches are available and using 1/16 inch or 1/8 inch felt wads is a possibility.
Another possibility experimented with by some is adding a sleeve inside the cartridge case to take up some of the valumn so powder charges are reduced but still keep the over all length the same. This is easier with turned cases.
