I've only killed 3 blacktails with PRB from a .50 cal Lancaster flinter using .498" balls over 95gr 3F Goex, first one was a 4-pt(8-pt eastern)at about 50-60yds standing quartering away looking back at me after I jumped him from his bed and he ran 30yds or so and stopped to see what went baah as him, the ball went thru and thru the upper shoulder nicking the spine, he piled up right there.
The next one was a forky standing broadside at 75-80yds, shot him thru the lungs just behind the shoulder, he turned an ran down hill about 60yds thru brush and was dead before I got to him, the ball passed thru and thru leaving an 1½" exit wound, and lots of blood on the latter 2/3rds of the trail to him.
The third one was a 3-pt bringing up the rear of line of does running past me, he was running broadside at about 30yds, I poked him thru the brisket, he stumbled and made a circle around me and headed back the way he come leaving a blood trail a blind man could follow. The ball went thru and thru and lodged in the off side knee, when he stumbled I thought maybe I hadn't hit him good specially when he kept going, but he was dead on his feet, just didn't know it. The ball was flattened out about 1" in diameter.