Getting into airsoft can be a bit of a learning curve, with lots of new terminology and processes to learn. When you start using airsoft guns, one thing you’ll have to get your head around is joules and how this relates to safety and good airsoft practice.
Understanding joules gives you a better perspective of your gun’s performance and will ensure you are staying on the right side of the law. Here’s what beginners need to know.
What are Joules?
First things first, what are we actually talking about here? In airsoft, joules measure a projectile’s kinetic energy, indicating how much energy a BB has after it has been fired from the gun. This essentially determines how powerful your gun is – we’ll get to FPS in a minute.
The Legal Joule Limit for Airsoft Guns in the UK
The 2017 Policing and Crime Act outlines the legal joule limit for airsoft guns in the UK, ensuring nothing too dangerous is used at skirmish sites. In this instance, joules are used as the defining factor of power.
For airsoft weapons that can fire two or more missiles successively without pressing the trigger again, the limit is 1.3 joules. When measured with a 0.2g BB, this equates to 375 FPS.
For airsoft weapons that discharge just one shot with every trigger press, the limit is 2.5 joules. When measured with a 0.2g BB, this equates to 520 FPS.
What is the Difference Between Joules & FPS
While both joules and FPS can give an indication of your gun’s power, they are measuring different things. FPS is a measure of velocity, changing relative to the weight of a BB – heavier BBs mean less FPS, but this has no bearing on joules.
So, although the FPS of your gun may change depending on the weight of your BB, the level of kinetic energy (joules) it produces should always remain the same – in theory.
What is Joule Creep?
We say ‘in theory’ because there is something known as ‘joule creep’, which refers to how much air is present to push the BB out of the barrel.
The perfect amount of air in the system ensures your BB leaves the barrel with the right amount of joules and energy. Too little air means your BB stops accelerating before it reaches the end of the barrel, losing potential energy. Too much air means your BB will leave the barrel with the proper joule rating, but you will have excess air in the barrel that gets wasted, potentially destabilising the BB and leading to less accuracy.
Although many AEGs experience minimal joule creep, HPAs and GBBRs can see it happen more commonly.
You can counteract excess air by using heavier BBs. This being said, doing so is often against site rules, as when you chrono at the start, you should be doing so with the system setup you intend to use.
To find out more about using a chronograph to test how powerful your gun is, see our guide, which especially helpful for airsoft newbies.
It is worth noting that it is possible to fire over the limit without intending to. Again, unlikely for AEG users, but it can be seen for HPA and GBBR players. Changes in the temperature can easily affect the gun’s output, often without the player even realising it.
Whether or not it’s intentional, even being in possession of a weapon that fires consistently over the legal limit carries severe criminal weight. If your full auto capable gun exceeds the specified limits, it could count as a Section 5 firearm, and possession of such carries a 5-year prison sentence.
This is why having a chronograph in your airsoft kit is so important, along with adhering to site regulations and keeping your gun firing in line with their chrono readings. Adjusting your gun after having the readings taken is against the rules and the spirit of the game.
Keep your airsoft guns firing consistently and legally! You’ll find everything you need here at Surplus Store, with a range of airsoft accessories, including all-important chronographs.