3F does work as prime and so does 2F, BUT and a big BUT it is, 4F is faster and Nul B is faster yet.
For me, I cannot hold the rifle any more, it is always moving. I try to time my ball's impact taking into
consideration the lock time. 4F works better for me when attempting to hit the X. On a big steel plate,
there is little difference. With anything other than 4F, the gun moves more after the cock is set free, than
any other slower burning powders in the pan.