Alias: It is possible that the slower rifling pitch may reduce scatter. Only way for sure is to experiment. No need to purchase over powder wads. You can punch them out of hard felt or even cardboard, with the same punch used to make overshot cards. Sometimes I just use a double overshot card...or double cardboard wad on top of the powder. Been doing this for many years, without issue.
icanuck: You may already be aware of this. But if not...here's some info that may help. For others, too. BP loads are usually measured in drams of powder. A dram equals 27.3 grains. So, it is very easy to calculate how many drams your powder charge is, by comparing it to the number of grains(by volume) your bp powder measure throws. Use the same measure to throw both powder and shot. For example: 3 drams: 80-82 grains(approximate) of 2 Ffg powder. Shot equivalent: 1 1/16-1 1/8 oz of 7 1/2 shot(approximate). This is my standard 12 gauge bunny load. Used for both muzzle loader and bp shotshells. I also quite often use a 56 caliber(28 gauge) smooth bore barrel, in place of my .50 cal. TC Renegade rifled barrel. Load: 2 drams/55 gr. Ffg. 3/4 oz 7 1/2 shot. A good bunny thumper.
In Brad243's case though, we are dealing with a bore that measures out to approximately 24 gauge. So...my 12 gauge loads are way too stout for good results in his rifle. Patterns will most likely be awful. 20 gauge loads are likely going to be a bit too hot, as well. While 28 gauge loads.. are likely a better place to start. In which case, a 2 dram/55 grain Ffg powder charge and approx. 3/4 oz of shot, may be the ticket. Or something in between 28 and 20 gauge. Only experimentation will tell the tale. I am interested in the results too...so Brad243...any info you can share is appreciated.
Chasseur may be onto something, too. The only way to be certain is to check with your provincial hunting regulations.