I sensed that this fellow has a preference for shooting conical bullets out of his Black Diamond and I believe that I have addressed his question.
When I originally bought my T/C Black Diamond and shot the gun with open sights, I used the 385 grain Hornady Great Plains Hollow Base conicals and was very satisfied with their accuracy as well as the way they loaded. Don't remember the exact group size (perhaps 3 inches max) with open sights at 70 yards. This combo worked well in any thicket and killed any deer standing in the way of a shot.
As I learned more about the "new" saboted bullets and their potential, I "updated" my muzzleloading techniques to using a scope along with a saboted round. I am no longer hunting a thicket, but hunting out of a blind along a field edge due to a job-related geographic move that I had to make. The sabot and scope extends my rifle's range, if I do my part correctly.
What do you want me to tell him....that he is making a mistake in shooting conicals out of a Black Diamond?
Not an oxymoron, but a preference.
Not everyone hunts with the same equipment, in the same manner, or with the same expectations.
But all methods will kill deer and all are enjoyable.