I spent 3 years trying to get around this problem,the last two were with Blackhorn.
I used to sight in by cleaning every shot while sighting in when I used 777 there was not much choice.
Last summer I finally work out a solution, it seems like overkill but it works for me.
I swab out the barrel with a 50/50 mix of #9 and alcohol fire 3 primers swab out again drying each time then fire 3 more primers and load.
This allows me to depend on the first shot hunting to be right on even at long distance. I use Montana X bore preservative to protect the bore and its part of the equation.