Erik in NJ wrote:
> What was the rationale for reducing the size of the balls over time?
In addition to what Ivan said ("better powders and rifling")... the desire to reduce the weight of the gun and the ammunition a soldier had to tote on long marches. Smaller caliber gun and ammo means significantly less weight. Or, you can carry a larger number of cartridges when they weigh less than the previous version.
Please note, especially, that I was referring to Military muskets. (When talking in my prior reply about the reduced calibers, I used the word Military three times in three sentences.) Civilian game-hunters used smaller-caliber muskets, rather than tote around a honking-heavy big Military musket. And by "Military" I mean Regulation-Issue ...in other words, the "standard" musket issued by the Regular (National) Army to its infantrymen. That does not include the hodgepodge of various-caliber civilian muskets carried by local Militia and "volunteers."
Also keep in mind that many of the 1700s/1800s smaller-caliber lead balls we relic-hunters find (.31, .44, .50-caliber, etc) were for pistols ...which were not "standard issue" for Army Infantrymen. (But of course, as many civil war soldier-photos show, a good number of soldiers brought their own pistol from home and carried it into battle).
To recap the ever-shrinking size of Military musket/rifle calibers in the past 200 years:
The British Army's standard-issue musket for Infantrymen during the American Revolution was the .75-caliber "Brown Bess" musket.
The US Army's standard-issue musket for Infantrymen from 1816 to 1854 was the .69-caliber Springfield musket.
The US Army's standard-issue rifle for Infantrymen from 1855 through 1865 was the .58-caliber Springfield rifle.
The US Army's standard-issue rifle for Infantrymen in 1866 was the .50-70-caliber Springfield rifle.
The US Army's standard-issue rifle for Infantrymen from 1873 - early 1890s was the .45-70 caliber Springfield rifle.
The US Army's standard-issue rifle for Infantrymen from 1892 - 1902 was the .30-40 caliber Krag rifle (a/k/a the US Magazine rifle).
The US Army's standard-issue rifles for Infantrymen from 1903 - 1961 were various models of .30-caliber (the .30-06, the M-1, etc).
The US Army's standard-issue rifle adopted for Infantry use in 1962 was the .21889 caliber (5.56mm) M-16
One additional point:
Readers, please keep in mind that a bullet's caliber is never the same as its actual diameter. The term "caliber" refers to the internal diameter of a firearm's barrel. For example, the .75-caliber "Brown Bess musket's lead ball was .71-inch in diameter ...because a musket is a muzzle-loading firearm. You cannot cram a .75-inch ball down the muzzle of a .75-caliber gunbarrel.