Welcome to the forum.
Your Remington 700 is an open breech design rifle I believe. I am guessing that it is not really made to shoot BlackHorn 209. There is a pamphlet BlackHorn has, or go to their website, they will show you what rifles can and CAN NOT shoot their powder. I am guessing yours is one of them.
Also are you really compressing that powder with a tight fitting sabot? I would get some Triple Seven or Pyrodex RS and try that powder in your rifle.