1. The Rifled Barrel
Older muskets had a smooth barrel. The Germans were the first to rifle their barrels. Someone got the bright idea to cut spiral grooves down the barrel. This would put a spin on your bullet. Once it leaves the barrel the bullet keeps spinning giving it gyroscopic stability. The stabilized bullet would be much more accurate.
2. Conic Bullets.
For a long time bullets were a sphere like a marble made out of lead. The problem with sphere bullets is that they aren't aerodynamic. No matter what side faces forward you get a lot of air resistance from all sides. The Minie ball was invented by the French not long before the US Civil War. Minie balls and later bullets would be better shaped so they would be more stable in the air.
3. Percussion Primer
Let's go way back. One of the earliest priming methods was known as a match lock. It looked similar to the picture above, but there was no primer cap. The hammer had a burning piece of rope called a match. You pulled the trigger and the hammer fell plunging the burning rope into the gunpowder to light it. This was effective, but dangerous because a burning ember could fall off the rope and set the gun off prematurely.
Later we have what is known as the flint lock. The hammer has a piece of flint and a tray you fill with gunpowder. You pull the trigger and the hammer strikes the flint on a strip of steel sending sparks onto the primer pan. The primer pan lights and the fire goes through the flash hole into the chamber to set the gun off. This was much safer than the match lock, but not as reliable. There would be a brief delay between pulling the trigger and the rifle going off. Hunters had a problem with animals seeing the flash of the primer pan and running off before the gun would discharge. This was still back in the days of muzzle loading so if you miss it takes a while to reload.
Finally someone came up with a small cap that had a shock sensitive compound that would shoot fire when struck. You put the cap on the gun. You pull the trigger and the hammer hits the cap sending a small jet of flame through the flash hole into the gunpowder. Now you had a priming method that was quick like a match lock and safe like a flintlock.
4. Enclosed cartridge
There were several paper cartridges through the ages that included powder and bullet but it wasn't till the mid 19th century that people figured out they could make a cartridge you throw into a gun. The paper cartridge would tear open, you pour the powder down the barrel, you ram the bullet down, you put the primer in place. The percussion cap was vital to the enclosed cartridge. With the percussion cap you could have a metal tube with the primer at the back, the bullet at the front, and the gunpowder sealed in the middle. Instead of the old task of loading everything one step at a time you could now fire, eject the old cartidge, slide a new cartridge in, then fire again. Soon lever, pump, and bolt actions would be made that could hold several rounds and by simply operating the action you could reload. Eventually automatics would be developed so the energy from the gun discharging would reload the gun for you.
5. Smokeless Powder
The final big jump was smokeless powder. Despite the name it DOES make smoke. It just didn't make as much as its predecessor. Before smokeless powder we had black powder. You may have heard the gunpowder recipe of charcoal, sulfur, and potassium nitrate. That makes black powder. It got the job done, but was inefficient. It left heavy soot inside your barrel which required frequent cleaning or you wouldn't be able to load the barrel at all. It also left a big cloud of smoke in front of you which could make it hard to see. Smokeless powder was developed around 1900. There are many different formulas of powder that can do different jobs. They burn cleaner than black powder so you get more energy out of your powder and less smoke. It's very important to remember NOT to use smokeless powder in a gun designed for black powder. The pressure differences can make your gun explode.
