The trick with CFE BLK is to compress it, a lot. It’s pretty hard to get an over pressure load before you run out of case capacity, but use common sense.
You can get enough, 14+ grains under a 240 SMK at 2.260” for better than 1400 fps. In an 10” barrel. Even a Berger 230 OTM. If this powder won’t cycle your AR without a suppressor it’s the gun.
Heavy supers are another place it can work, but you won’t get the velocity of 1680 or H110/296.
That said, it can be accurate, but it’s a poor choice in my opinion. 10% more powder to get 10% less velocity only to get more gas, smoke, noise and carbon. It does work well in some other cartridges.
Subs work much better with long heavy bullets no matter what the powder. Load density below 80% just leads to high spreads. Pistol powders like #9 and sadly my favorite that has been discontinued, N105 are good example of clean, quiet and consistent.
I wrote this up when CFEBLK first came out. What’s interesting is that many of the hot shot utoobers were praising it at the same time. 9 years later, people are finally reporting the same.