SO..., when this was first posted, I remembered a magazine article decades ago where a fellow named Mark Baker mentioned his hunting load. A .490 ball and 50 grains of powder. Mark is also the author of
Sons of A Trackless Forest, was a longtime column writer for Muzzleloader with his column titled
"A Pilgrim's Journey". Neither of those two writing credits necessarily gave Mr. Baker any hunting knowledge, but... he was often out with, and shown hunting skills by, men who pretty much lived in the woods with their flintlocks. He couldn't do that if he was "unethical".
Well..., GUYS FREAKED OUT in the chat rooms about how bad that was to hunt deer. Funny..., Mr. Baker NEVER mentioned the distance. At 150 yards, yes for me, that would be too light a load, but at 40 yards, that would likely
"get 'er done".
So with the OP's specifications, and the results which proved him correct in his thinking, no harm ; no foul. I couldn't do it, but that's because my state requires a minimum load of 40 grains of powder in a black powder hunting handgun, YET I would be legal with that load and a 90 grain .390 bullet from a single shot pistol.
In fact I plan to do it, but I'm planning on a Pedersoli Bounty pistol in .45, flintlock (they have a 16" barrel folks) and I think I will fashion a shoulder stock on it as well, like an 18th century version of the fictional character Colonel Mortimer.... (HEY the pistol's a fantasy flintlock so the shoulder stock isn't harming a thing)
Lee Van Cleef with a more modern version as Colonel Mortimer .... AH Hollywood, the revolvers were too modern in this movie. It was still supposedly the 1860's
Well the OP had a very nice hunt and a very nice deer. CONGRATS
LD