Dave , I have to agree with Builder, I have found that to tight blows the accuracy. My rule of thumb on it is that is that it needs to be tight enough that I need both hands on the ramrod to push it down and that if I feel like I need to pound on it it won't shoot good. I truly believe that a lot of these people settle for 1.5 to 3 inch groups just because they never learn to find that narrow slot where just the right amount of pressure gives the barrel what it needs to stack bullets at 100 yds.
I have found this to be true of all powders Blackhorn is the most sensitive to it but they all shoot best at that same set pressure.