MilSim is an abbreviation of Military Simulation., and there are many applications of MilSim: airsoft games, military training, and video games similating military scenario's and tactis. Weapons used in MilSim are commonly referred to as airsoft guns. They are made to resemble real guns from many time periods.

Popular reenactments include World War II battles using weapons like the tommy gun and smoke grenades. Military simulation battles are popular but there are other types, such as a standard battle using a preset number of hits before you are "dead" there is also airsplat which is a form of play using 6mm airsoft paintballs. When playing a military simulation, game people are encouraged to wear clothing that resembles the time era, although this is usually not mandatory.

Airsoft: The sport of Airsoft started in Japan during the early 1980s. It was illegal to own firearms in Japan but there was a significant interest in them, so a company started producing spring-powered replicas of firearms that fired 6mm, plastic BBs. There are some people who insist that Airsoft originated from the early days of paintball, when there were paintball guns that fired .22 caliber paintballs, but we will not delve into that subject. During the latter part of the 1980s the sport migrated to neighboring countries such as Hong Kong, Korea, Taiwan, and the Philippines. Airsoft started appearing in North America and Europe during the middle of the 1990s but it is only during the last 2-3 years that the sport started thriving in these venues.

There are 3 major types of Airsoft guns: Automatic Electric Guns (AEGs), Gas-Powered, and Spring-Powered.

The most popular of the 3 types is the Automatic Electric Gun. The creation of the AEG is partly responsible for Airsoft's "boom" during the late 1990s. Basically, an AEG is powered by an on-board Ni-Cad battery (similar to hobby R/C Cars), which operates a motor that turns gears inside the gun to compress and release a piston, which in turn creates the blast of air needed to propel the 6mm BB through the barrel of the gun. This system allows the gun to efficiently generate the power needed to support the fully-automatic features of most AEGs and the result is a realistic Rate-Of-Fire (ROF) of anywhere from 600 - 900 Rounds-Per-Minute (RPM), once again mimicking the capabilities of real steel firearms. This is the airsoft gun of choice for most skirmish veterans. The reigning king of the AEG manufacturers is, undisputedly, Tokyo Marui of Japan, due to it's high-quality construction and an immense number of after-market support and upgrades for it's guns.
For more information: www.airsoftretreat.com/about_airsoft.asp

Paintball: The evolution of paintball into the modern sport that it is today took place fairly quickly in comparison to most other sports. The history of the paintball gun begins in the early 1970s, when it was used as a tool for marking trees and livestock. In 1981, twelve friends played the first recreational paintball game using these industrial paintball guns on a field measuring over 100 acres. One of the first names given to the sport that we now call paintball was “The National Survival Game.” This name reflects the nature of paintball as it was first played – a small group of friends getting together in the woods to play total elimination games. Sometimes the friends broke into teams to play each other, but most games were “every man for himself.”

The first outdoor commercial paintball field started in 1982. The first indoor paintball field followed in 1984.The fields allowed large groups of people to meet in one place to play, and the business owners were pushed to develop new and exciting ways to keep these paintballers entertained. This drove the development of new scenarios and styles of playing.

The biggest style of play change to come about because of commercial fields was the “bunker-style” game. Smaller fields let players start the action quicker, instead of having to stalk through the woods for 15 minutes before seeing anyone. Also, players purchased more paintballs when they were in a constant firefight, which made the commercial fields more money.

Today, commercial paintball fields are everywhere, but there are still a large number of people that prefer playing paintball out in the woods. While outlaw paintball is generally much cheaper, it is also more problematic than paying to play at a commercial field.
For more information: paintball.about.com/od/gametypes/a/gamehistory.htm