Consistency is the key to accuracy. Proper repeatable form is as much of a factor as the proper load recipe. Look at high power shooters, they shoot 1000 yards with open sights. I can't do it but some can. Personally, I have no use for open sights. I use optics.
I have not had problems getting MOA accuracy with 3 different guns (TC Black Diamond, Rem 700, custom Rem 700) using 150 gr of Pyrodex pellets, musket caps, and PR QT40 bullets. When I went to 209 primers, the groups opened up to 3".
Finding the proper recipe for your gun can be challenging. I have been messing with a Knight Disc Elite .50 cal for years to find a combination that will shoot at the speeds I want as accurate as I want. So, I hear ya. By the way, a recipe of 100-120 gr of BH209, SST 250 or 300 in a Harvestor sabot, shoot great in both my Omega and Triumph. This load is popular with many TC shooters on ML forums.