The best commercially made balls I've found are those made by Speer or Warren Muzzleloading. Hornady is okay, but I always seem to find a few slightly out of round or with swaging marks in each box of Hornady.
Warren Muzzleloading is in Arkansas. Like Speer and Hornady, its balls have no sprue so there is no nub to dead-center straight up before loading.
You may order Warren Muzzleloading balls at www.warrenmuzzleloading.com
Most sporting goods or gun stores stock Speer or Hornady balls.
Remington also makes a lead ball, brass-plated. They're good too and have no sprue. They're not often seen on the shelf. At least, not around the Salt Lake City area.
Interestingly, Remington claims that this brass plating helps to eliminate leading!
Um ... scuze me, Remington .. but that lead ball is enclosed in a patch! It never touches the bore.
And if a plated ball is used in a cap and ball revolver, the plating from the area that touches the rifling is removed with the ring of lead shaved from it.
Sheesh. What a load of advertising hooey.
But the Remington balls with their brass plating have one advantage: few people seem to use them, so they're readily recognizable when recovered.
If you use them, and your buddy doesn't, and you both fire at a deer --- you'll know who got it if you recover the ball.