Yes, you do use airsoft guns for both, but there still is a huge difference.
I decided to write this article because I frequently see airsofters saying that they love mil-sim, later, when describing the supposedly mil-sim scenario, it turns out it was just another paintball style airsoft battle. People used high capacity magazines and poured thousands of bbs around the area.
I am only going to use terms “competitive airsofters” in a descriptive way for lack of better words, not in any derogatory way.
What is airsoft?
Technically speaking, airsoft is a game where participants shoot each other with weapon replicas using gas or air to propel 6 or 8 mm bbs (ball bearings) made out of plastic. I am not going to talk about its history, since you can find that anywhere on the internet.
There are basic rules, but mostly, airsoft is a competition sport, unlike mil-sim, which is strictly scenario based.
Mil-sim, shortcut for military simulation, as its name implies, is a type of game where there are real military strategies used, usually incorporates machinery, scenario, airsoft teams that study and simulate real units and armies and medium to low capacity magazines.
A mil-sim operation usually is for a large number of players who take part in given objectives and try to reach then using good teamwork, co-operation with other units and support.
In mil-sim scenarios there are at least two sides taking part in the conflict and both try to reach their own objectives, unlike competitive airsoft where one side usually attacks and the other defends. In mil-sim shooting is not the only option. There can be kidnapping, negotiation, special mid-night operations, etc. People kidnapped (and this is a scenario I have experienced myself) can even be forced to water boarding and other forms of torture under the surveillance of a trained doctor (it was part of the scenario and people willing to go through that had a special card with them which, when found by the captor, gave them a special right to SLIGHTLY torture the prisoner), which is, in a way a great experience.
I highly doubt that this would ever happen in competitive airsoft.
It is very likely that during a mil-sim scenario, you will not see bb sprayers. As you are given only a certain amount of ammo for the whole game, you cannot afford to spray senselessly.
Mil-sim airsofters are usually people dedicated to what they do and in many cases soldiers or former soldiers. Most of those people have sunk more money into their equipment then some people in their cars. I can guarantee that most competitive airsofters would not stand a chance against mil-sim airsofters.
Competitive airsofters mostly rely on having more ammo in their high capacity magazines than others. Mil-sim airsofters rely on their team members and mates.
Mil-sim airsoft is not about competition, about shooting at other people, it is about co-operation, about simulation of something you will not experience every day, it is about being part of something extraordinary, friendship, and the memories. I mean, what could be better than to go to an assault sitting on the hull of a BMP.
During a mil-sim game, you do everything in-game. Eating, bathroom, sleeping, etc. There are no breaks.
So, I guess, there are the main differences between competitive airsoft and mil-sim airsoft.