Thanks all.
Regarding questions about load, I used a .50 cal Hornaday Great Plains 385gr. bullet with 80 grains of goex FFFg. The shot was about 20 yards. The three previous bulls I have taken with this rifle were with patched round ball. For years I had a hard time with accuracy of conical/slugs, and still do a bit.
It was more of an accidental ambush than a stalk. I was sneaking up a brushy ridge and had been approaching some cows, which were also legal to shoot. This bull was bugleling in full rut, and suddenly the cows came stampeding staight at me with this guy screaming at their heels. Don't mean to vulgar, but he might have departed his life, "in the mood" so to speak.