I applaud you for your concern about the loss of an animal you hit. It still bothers me about one i lost many years ago.
TBS, it is going to happen to us from time to time.
Muzzle loading guns are all about bullet placement. We have to know going in that we are using challenging equipment, and there may be a good long chase.
The gun you describe is a capable one. You could have had the same results from many other setups. A bad hit is a bad hit even if you aimed at the right spot. We all know what happens in the bush when our bullet hits a small branch.
Good luck on future hunts.
For the message of the Cross is foolishness to those who are perishing, But to us who are being saved, It Is The Power Of God. 1Corinthians 1-18