[Jeff Higgins]

It's all about the ballistic coefficient of their respective projectiles. This coefficient is used to calculate deceleration, with some mythical artillery projectile arbitrarily assigned a value of 1.0. All sporting arms projectiles will be some fraction of that, depending upon how "streamlined" they are. Heavy for caliber, boat tailed spitzers have the highest ballistic coefficient, some of them exceeding .600. The higher this number, the slower they decelerate. Average hunting projectiles can run anywhere from the .300's up into those .600's. A typical 180 grain .308" diameter boat tailed hunting spitzer will be somewhere around .500, so let's use that for our comparison.

The ballistic coefficient of a .495" diameter round ball of 180 grains weight is only .070. Yes - zero seven zero. The affects of these widely disparate ballistic coefficients on their external ballistics is quite stark. Let's take a look.

Muzzle energy for a 180 grain projectile from the .30-'06 at 2,700 fps is 2,912 ft lbs.
Muzzle energy for a 180 grain projectile from the muzzle loader at 2,000 fps is 1,616 ft lbs.
Already a 1,300 ft lb difference. But it gets a lot worse...

Velocity at 100 yards with the bullet from the '06 is still 2,519 fps, energy is 2,536 ft lbs. It still has 87% of the energy it had at the muzzle.
Velocity of the round ball at 100 yards has dropped to only 1,124 fps, energy down to 510 ft lbs. It has less than one third of the energy it had at the muzzle.
It gets worse...

At 200 yards, the '06 bullet is still doing 2,345 fps, with 2,197 ft lbs of energy, 75% of what it started with.
The round ball is now down to only 793 fps and 254 ft lbs of energy, only 16% of what it started with.

Beyond that is the exceedingly low "sectional density" of the round ball. This is a measure of how much it weighs vs. its cross section. The longer the bullet, the higher its sectional density. A round ball is obviously about the shortest projectile we can fire, short of some sort of a contrived disc or something.

Sectional density is a very clear indication, given similar constructions, of different bullets' relative abilities to penetrate. The heavier a bullet is for a given cross section, the more deeply it will penetrate at a given velocity. This is kind of intuitively obvious.

Essentially, the round ball is the worst possible shape both aerodynamically and with regards to its ability to penetrate. Combining both of these shortcomings in one projectile leaves us with a very poor hunting bullet. Or fighting bullet. We realized this some time in the early to mid 19th century, and started experimenting with elongated bullets. By the time the 1870's rolled around, we had .45 caliber bullets exceeding 500 grains in weight for use in both muzzle loaders and the then new breach loaders.

So, while the round ball is historically correct, kind of "romantic" (at least for shooters), even during its heyday the guys using them knew they needed something better.