Howdy
I load all my Black Powder shotshells for CAS on my old MEC Jr.
I do not use modern plastic wads, I use separate wads I buy from Circle Fly.
http://www.circlefly.com/
You can also buy them from Track of the Wolf.
https://www.trackofthewolf.com/
If you want to use modern Plastic wads, the best wads to use are the old Winchester Red Wads. Unfortunately Winchester does not make them any more, but Claybuster makes a good replacement wad. The 7th one down, CB1138-12. This wad is good for Black Powder because it is short. Leaves more room for the Black Powder charge than modern wads do.
http://www.claybusterwads.com/index.php/winchester-style
Here are the components I use for my BP shotshells. I like to use the Remington STS hull, because they are slippery and extract the best out of our SXS shotguns in CAS. Any shotgun primer will do, I usually use Winchester 209 primers. It does not matter what primer you choose, Black Powder is easier to ignite than Smokeless, so any primer will work. I use the standard 1 1/8 ounce charge bar that came with my MEC. I like to use #8 shot.
About the powder charge. There is an old rule of thumb with Black Powder shotshells called making a Square Load. What this means is the powder charge should be about the same volume as the shot charge. Forget about weight for a moment, just think in terms of volume for now. If you put too much powder into a shell for the amount of shot, you will tend to blow the pattern. If you keep to a square load, you will not blow the pattern. If you put less powder by volume into the hull than shot, this is also OK. It is when you put in too much powder that you will tend to blow the pattern.
I use 4.3CC of FFg in my shotshells. This works out to about 64.5 grains with my favorite powder, Schuetzen. Because not all powders weigh the same, you will get slightly different weights of powder depending on which powder you use. It does not matter much, I like Schuetzen because it burns a little bit cleaner than Goex and is not as expensive as Swiss. 64.5 grains works out to about a 2.35 dram load, which is relatively mild and will not blow the pattern with 1 1/8 ounces of shot.
Despite what you may hear, I never drop the powder directly out of the bottle on my MEC. I will not put powder into a plastic bottle. Instead, I dip the powder in, using the 4.3CC dipper from a standard Lee dipper set. The 4.3CC dipper is the largest dipper in the set.
https://leeprecision.com/powder-measure-kit.html
NO SMOKING! OBVIOUSLY!
To dip powder properly, pour about 1/2 pound of powder into a coffee cup. Use the dipper like an ice cream scoop, scoop the powder up. Use a consistent motion each time to keep the charges the same. The powder will be mounded up on the dipper. Do not tap the dipper to settle the charge. This will lead to inconsistent charges. Using a piece of card stock, scrape the powder level. Then using a funnel dump it into the hull.
After dumping in the powder, I seat a Circle Fly 1/8" Over Powder card. Then using a 1/2" dowel I compress the card onto the powder until I hear a slight crunch. Then I seat a Circle Fly 1/2" Fiber Cushion Wad. Next I dump in the shot, using the throw bar on my MEC. Because my charge does not quite fill the hull all the way, I next seat a .025 Over Shot card on top of the shot. This keeps my crimp flat and prevents any shot from escaping the crimp. Finally I crimp normally.
Using this method I can turn out about 4 boxes of shells in an hour. Not as fast as loading Smokeless, but it works for me.