I am willing to bet that your charge WAS wet, regardless of what you now think. Try doing some penetration testing at 90 yards with that gun and charge, and that PRB. I am willing to be it penetrates through lots of wood, or whatever you use. at 90 yards, the ball should still be going over 1,000 fps. and a 230 grain ball at 1,000 fps. is going to kill any deer, breaking that neck bone. It will also knock the deer down.
I had a similar experience with my .50 cal. flintlock but shooting down at a small buck that walked under my deer stand late one afternoon towards the end of my deer season. I had the gun loaded all day long, beginning with damp conditions. By afternoon, the conditions had dried, and the sun had warmed me up, too.
My ball bounced off this small yearling's shoulder, not leaving any blood, but did knock him down. He got up and walked away at a fairly good gait, but slowed down about 50 yards away. The shot sounded "almost " normal, but the more I tracked that deer, finding not only NO BLOOD, but not even a limp! and the more I thought back to that shot, the more I realized that it didn't sound right at all.
That evening, when I cleaned the gun at home, I had substantial unburned powder residue in the barrel- much more than usual. Its always possible that your experience has another explanation, and somehow shed much more velocity over 90 yards than should happen, but I have my doubts.
I am glad you got that second shot at the buck, and your hunt ended with perfection. That is a very nice trophy, and a credit to your ability and tenacity as a hunter. Congratulations. :hatsoff: