I bought a New Englader in 54 cal years ago with the idea of picking up a 12 ga barrel for it down the road to shot turkeys. I think the barrrel is pretty much an open choke to make it possible to get a tight fitting wad and overshot wad down the barrel and still remain tight fitting.
Instead I picked up a Navy Arms double 12 at a gun show. I tried it out and had terrable patterns. I tried to find shot cups that were not split to no avail. When I tried taping standard split shot cups I ended up getting an oval pattern, better but not good.
One night I called Cabela's customer service. The gal that answered turned me over to a guy that went way above what could be expected. He found a muzzeloader shot gun kit that had cups wads-- every thing I needed. The cups were uncut. It said in the directions to split them but I left them solid and got a good pattern out to 25 yards. The cup would go through the cardboard my target was on at 25 yards.
Thsi is the info off the paperwork that came with the kit.
Cabelas black powder package
MANUF. BY www.ballisticproducts.com
I have been on BaIlistic products web site but could not find the shot cups listed. I have no idea if Cabelas still has the kit but it would be worth a try giving them a call.
I used an equal measure of powder and shot using the cup as the measure. The paper work says the cup should hold 1 1/4 oz of shot. If I remember right it held right around 100 gr of pyrodex.