Cant beat the Hornady.
I had the same experience you did with the Cowboy loads. I think I tried Buffalo Brand??? from Cabelas. The best thing I can say is I was able to hit paper at 25 yards and ended up with 40 empty brass.
was shot with Leverevolution in a Winchester 1885 @ about 140 / 150 yards.
Broke both front shoulders and stopped just under the skin on the exit side.
Didn't kill it, but it dropped right there and couldn't move.
With that same gun and load, I shot a Black Hawaiian sheep semi quartering away. The entry hole was the size of a tennisball and the exit took the entire shoulder off and was hanging by the skin.
Maybe it was just the way it hit.
I also run them in my Marlin full size lever action (not a guide gun).
Both are open sights and group 3" or less at 100 yards if I am having a good day.