Back in the ancient days bullets were round balls. We'll skip straight into the "rifled" era of firearms to make things simple. A round ball with a greased patch rammed tightly into the bore of a firearm was the most accurate projectile on the battlefield (or hunting field) for a long time. Round balls are still every bit as deadly as they were four hundred years ago, even if tissue disruption varies from none to a lot. A half inch or larger hole in anything is nothing to sneeze at.
Round balls were very accurate at reasonable ranges. However round balls are not very aerodynamically efficient, which limited the effective range. The next invention was the Minnie Ball (named after the French guy whose name has that little accent mark I can't figure out how to put into text). The minnie ball is a very modern looking bullet, it has a conical open base that expands when the powder is touched off to engage the rifling. A pointed nose made it more aerodynamic. The minnie ball took a horrible toll in the Civil War.
At the same time as the minnie ball was killing lots and lots of Americans, metallic cartridges loaded with black powder were killing lots and lots of buffalo. I know the timing isn't exactly right here historians, but I'm telling a yarn so give me a little creative license. The bullets used were "paper patched" to keep the lead from fouling the bore with lead, and accuracy was legendary. The Sharps rifle firing paper patched bullets gave us the term "sharpshooter" which we still use to this day.
Of these three black powder, pure lead, bullets, all three were accurate, with the paper patched metallic version the most accurate, followed by the minnie ball, and followed by the round ball.
Penetration was quite good, assuming equal weight for all projectiles, the paper patched and minnie ball would out penetrate the round ball (the round ball having the lowest sectional density).
Tissue disruption with a round ball is usually a straight wound channel. Round ball projectiles do not generally deform much at all unless they happen to hit bone, and then expansion will be irregular and unpredictable but still very deadly. The minnie ball expanded a bit and paper patched bullets would expand quite a bit, "to about the size of a half dollar" in some cases if you believe the oral history of the buffalo hunters. The paper patched bullets win in the expansion department because the center of mass of the bullet was further rearward, allowing the nose to deform more before the center of mass "caught up" with it.
Now as progress continued, smokeless powder took over, and cartridges could be made smaller, fire more shots without the barrel fouling beyond use, and velocities could be increased. It is as this point where the "big bullet at moderate velocity" school of thought of the Buffalo Hunters meats Roy Weatherby with his "velocity is King" idea.
We will stay with lead bullets for now, but suffice to say that only paper patched and “gas checked” metal bullets were able to handled the added velocity of smokeless powder. A “gas check” is a disk of copper (or aluminum to some folks that make their own) that protects the base of the bullet from the effects of the propellent gas. Bullet makers have called modern “cup and core” bullets, “full length gas checked.”
In small arms, these lead bullets, either paper patched or gas checked, have plenty of lethality at reasonable ranges. The limiting factor for long range use is the poor aerodynamic shape of the lead or lead alloy projectile.
The picture shows a few of the more common bullet profiles, flat nosed, round nose, and wadcutter. Note that the driving bands are separated by lube grooves. The paper patched bullet above has solid sides, and gains a small bit of aerodynamic advantage as a result.
That is pretty much it for "state of the art" lead rifle bullets. Not a lot has changed in the last century, and if you take up bullet making (casting or swaging) as a hobby you can kill things every bit as dead as the fella paying over a buck a bullet for some premium pills. Please note that alloying the lead will change the expansion characteristics, to the point where some bullets will shatter or crack instead of expand.
Now let us talk handguns. Handgun velocities are slower, which means to get penetration you need momentum. Lead bullets such as; wadcutter, round nose, truncated cone, all give you adequate penetration. What they will not do is reliably expand and disrupt tissue. So someone got the idea to turn a hollow base bullet around, and create the first "hollow point" bullet. The idea is that the hollow point will hit tissue, fill up with stuff (especially liquid) which will hydraulically press the lips of the cup outward, causing more tissue disruption.
The lethality of hollow points is hard to quantify, as it is a feature that affects only the second and third part of lethality, penetration and tissue disruption. Very few hollow point bullets will "under penetrate" at normal handgun velocities, but something truly weird happens as you increase velocity, penetration declines as the bullet expands more quickly initially and encounters more resistance to the larger surface area. If you push a hollowpoint pistol bullet fast enough, it will come apart quickly in tissue instead of penetrating deeply. However, at normal velocity, the expansion does not significantly degrade penetration to the point of decreased lethality, and the increase in surface area aids in tissue disruption.
It is interesting to note that the Webley "Manstopper" bullet was a hollow base hollow point cylinder bullet. The hollow base sealed against the bore the way the old minnie ball did (not that old at the time really), and the hollow point caused reliable expansion even at sedate Webley velocities.
Now, as a closing note, I want to address the question, "Why Lead?" The answer is that Force equals Mass times Acceleration. If you want to increase force, you either have to increase Mass (meaning use something heavier, ie, more massive. Lead is also very maleable, so it can conform to the bore and get a tight gas seal. Replacements for lead, denser like depleted uranium and less dense like copper, have been used, which will be discussed in an upcoming post at some point.
Some handy equations to remember.
Force = Mass X Acceleration
Momentum = Mass X Velocity
Energy = 1/2 Mass X Velocity Squared