Q: What are bullet cartridges? A: Bullet cartridges are a combination of a projectile (the bullet), a propellant (gunpowder, for example) and a primer (the explosive cap), all contained in one metal package.

Historians count the machine gun among the most important technologies of the past 100 years. As much as any other factor, it set the brutal, unrelenting tone of World War I and World War II, as well as most of the wars since that time. With this machine, one soldier could fire hundreds of bullets every minute, mowing down an entire platoon in only a few passes. Military forces had to develop heavy battle equipment, such as tanks, just to withstand this sort of barrage. This single weapon had a profound effect on the way we wage war.

In light of their monumental role in history, it's somewhat surprising how simple machine guns really are. These weapons are remarkable feats of precision engineering, but they work on some very basic concepts. In this article, we'll look at the standard mechanisms machine guns use to spit out bullets at such a furious rate.

High-tech Weapons on Discovery Want to know more about stealth weapons, mine destroyers, attack submarines and sniper rounds? Tune in to "FutureWeapons" on the Discovery Channel.

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