I have a couple of renegade ex-black powder shooter friends who are having very good results with Blackhorn 209. It shoots accurately and the arduous cleaning between shots is eliminated, so they think it's worth the extra expense and the possible excommunication from the Black Powder community, if any of the Fundamentalists find out. But they are in a completely different area of inquiry than black powder. 209 was reportedly formulated to require 209 shotgun primers in in-line muzzle loaders, so it would need quite a kick. Putting a primer wad in would be counterintuitive, of course.
You might go to standard Large Rifle primers (no wad) if you want to check out milder ignition for accuracy improvements. I would suggest a minimum distance of 300 yards because, as Bruce Moulds says, the basic problem is vertical stringing and this may not be apparent at shorter ranges.
40Rod, I can't think of a place where your signature line is more appropriate that in this discussion!
Another friend did quite well for himself going to a monthly BPCR Silhouette shoot. The other shooters would ask him about his loads and when he mentioned Primers, they'd say, "No wonder your scores are so low! Nobody shoots those Standard primers; we're all shooting Magnums! It's the only way to go!"
He'd ask them if they had any Standard primers left. "Oh, yeah; I got 3/4 of a case of them; don't know what I'm going to do with them, since they're worthless to me." My friend would mention a very low price and go home with the "useless" primers.
Next month he'd be shooting Magnum primers, and the same experts would go "What's the matter with you? Nobody shoots Magnum primers; the only way to go are Bench Rest primers!" The friend would negotiate a low price for the remaining Magnum primers these people had and take them home. Next time it would be Pistol primers, next time something else. He'd buy all the "worthless" remainders he could.
The friend may never win the Nationals at Raton, but he has all the Primers he'll ever need, at way, way below wholesale.