Hi Loiner , I also have just received some 25mm thick pads from aliexpress to use on my Pedersoli percussion 12 bore , Trying to get 12 bore cushion wads past the choke is nigh-on impossible but hard felt wads cut to .720" fit perfectly as they are slightly flexible and when cut in half to 12mm are ideal.
If you are going to use in a drill press I can make you an cutter .45 or .36 to use in the drill if required.