Get Started in Airsoft – Is Your Gun Within the Limits

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Category: Airsoft 101

Is your gun within the limits?
Last month we looked at the process of buying your first gun legally in the UK and we revealed that it’s perhaps a little more complex than you might imagine. This month, we are going to look at the next step, something we touched upon last month but also something that deserves a little more time and attention. This month we are looking at the velocity or FPS of your BB Guns and Airsoft Guns, how to measure it and how to change it.

Why Have Limits?

In the UK and certainly all around the world, Airsoft Guns are subjected to limits when being used in skirmishes to shoot at each other. These limits vary considerably depending on where you are in the world, but generally, they are there.

Firstly, limits are there to prevent any terrible kind of injury. If airsoft guns only output BBs up to a certain level, we can be assured that even from close range, nobody will go home with a leg hanging off or worse. This isn’t to say the limits we currently use are below the point it takes to cause an injury. Even with guns well inside the site limits imposed, we’ve seen teeth knocked out and BBs embedded in soft skin from time to time. It’s rare but it happens. Coincidentally, the level of energy it takes to irreparably destroy a human eyeball is around the “1 Joule” mark or in airsoft terms, 328fps on a .20g BB. That’s precisely why proper eye protection is a vital and essential part of airsoft.

The limits in airsoft are not just imposed to keep things safe and on the whole, bearably comfortable. The limits imposed are also a great addition to the game to keep things sporting. With time, effort and money invested, a game of airsoft with no limits would quickly become uninteresting because it would simply become dominated by players or teams with more money to throw at more upgrades. Who would willingly want to play a game like that? I can’t imagine many would.

So in terms of relative safety, insurance and to preserve a level of sporting participation for the experienced and new-comer player alike, site limits are a very good idea, but what are they?

What Are the Limits?

As mentioned in the opening few lines, site limits vary slightly up and down the UK and the only way you can be totally sure of them is to talk to your site operator.

Generally speaking, the limits we use are loosely based on the principle of a 328fps (1 joule) limit with a variance allowance of 5%. This gives an upper limit of around the 345fps mark. A few years ago this was just about the standard model for the country but in the last 5 years, it’s fair to say the levels used by some site operators have crept up. For simplicity’s sake, some use a simple upper limit of 350fps where as others have jumped up to 370fps but enforce “semi auto only” rulings in close quarters.

The limit here is the one used for the “regular” types of airsoft gun, assault rifles for instance. For certain types of gun, like bolt action sniper rifles or semi auto-only electric rifles, the limits might be higher. It’s not uncommon for them to be as much as 500fps but with a “Minimum Engagement Distance” or simply an agreement not to fire at players within, for example, 20m.

UK Average Site Limits

  • Full auto rifle, sub-machinegun or pistol – 345fps
  • Semi auto “DMR” – 400-420fps
  • Bolt action sniper rifle – 500fps

What to Test?

When testing these limits, the convention in the UK is to take a reading of “feet per second” or what we have referred to here as “FPS” because it is the simplest and most realistic way of measuring the output of the gun, however a velocity reading can be a little misleading. Because BBs come in a variety of weights, the speed of the projectile is often irrelevant and it’s the energy level it is propelled at that is of most interest. Are you confused yet? Don’t worry, we’ll explain…

A lighter BB will travel faster when fired with any given airsoft gun than a heavier one, but that gun is still firing with the same energy level. FPS readings are historically taken with a .20g BB but with players using up to .43g BBs commonly, the limit in FPS changes dramatically. 

Using our above assumed averages we’ll convert the FPS readings into slightly more manageable readings using one of the many online airsoft FPS calculators and converters, although the math behind the conversion isn’t massively complex.

UK Average Site Limits Using Differing BB Weights

0.20g BB – 345fps – 1.1 joules
0.23g BB – 322fps – 1.1 joules
0.25g BB – 308fps – 1.1 joules
0.28g BB – 291fps – 1.1 joules
0.30g BB – 281fps – 1.1 joules
0.36g BB – 257fps – 1.1 joules
0.40g BB – 244fps – 1.1 joules
0.43g BB – 235fps – 1.1 joules

As you can see, as the weight of the BB increases, the velocity decreases, but the energy remains the same.

Why Use Different Weights?

The golden question then must be, “Why do people use different weights of BB?” With little knowledge of the subject, it’s easy to see why somebody would come to the conclusion that you simply use a heavy BB to bring the velocity down. That’s largely the fault of convention because so much emphasis is placed on the “Feet Per Second” reading and so little is placed on the “Joules” reading. Without knowing a little more about it though, the worst case secanrio could conceivably be a player filling his magazines with 0.43g BBs and tuning to the 345fps limit. That would result in a gun with 2.36 joules of energy, over double what the actual limit sits at!

The actual reason many players will opt for heavier BBs is for greater accuracy and in some cases, more range. A BB with more weight will be less influenced by factors like wind and air resistance and although it sets out slower at the muzzle, might actually be travelling faster towards the end of the trajectory because it will loose speed more slowly as it travels through the air.

This is why players sometimes assume that a heavier BB hurts more than a lighter one. It’s simply that at longer ranges, heavier BBs retain more momentum than a lighter one.

How to Test

Chronoing or testing your gun is something you need to get used to doing as an airsoft player. It’s a great indication of not only the power of your gun, but also how healthy it is. A decent gun with consistent, quality ammo shouldn’t have a variance of more than around 20fps from shot to shot, if it does, this is a telling sign that something is wrong. It could be anything from a dirty inner barrel to a worn piston or poor airseal, but consistency is the key to a good gun and accurate shots.

Testing should be carried out with the type of ammo you wish to use at the time, and the hop set accordingly to achieve a reasonable flight pattern. If you are using heavier BBs, it’s important to make this known. Failure to do so is essentially cheating and could result in you being ejected from the site.

The Hop-Up

Because of the way the hop-up unit in your gun works, generally, the more hop you apply, the more resistance the BB has to overcome when pushing past the “nub” and the slower it will leave the barrel. The effect can be as much as 30-40fps. Setting your hop-up in a realistic manner is something that should be done when chrono testing and if you crank on the hop to pass through with a lower reading, it will soon be evident to the marshal.


There are some variable that can have an influential effect on your chrono results. One BB brands sold as .20g may well vary very slightly from another brand and the same applies to all BBs. In fact BBs can vary from batch to batch so we wholly recommend factoring this into your upgrade plan. It’s pointless tuning a gun to fire at 344.9fps on a .20g BB if the natural variance of BBs will more often than not take your gun over the 345fps limit. That’s why traditional the variance of 5% was factored in and wise players take it into account. Essentially, 345fps is the upper limit and shouldn’t really be considered a “target” to aim for. There are very few instances where a 330fps gun user will be disadvantaged by a player using a 345fps gun so you should certainly weight up the pros and cons of taking it to the max.

How Not to Test?

If you venture online, you’ll probably find a few suggested ideas for a “poor man’s chrono”, most of which are ideas about using an empty drinks can as a target and measuring the amount and area in which a gun can shoot a BB clean through. These ideas are nothing more than a waste of time and are very inaccurate even when it comes to getting a vague idea of the power of your gun. Unfortunately, in terms of testing a gun, the way to do it is to fire it through a chrono. It’s the easiest way.

The Laws

With the practical side of things cleared up, there’s now the murky subject of the law surrounding the power limits of an airsoft gun. As the laws governing RIFs stand, they are based around the outward appearance of the item, disregarding its ability to fire any sort of projectile and whilst it’s true that a study was commissioned to distinguish the threshold of beyond-trivial damage caused by an airsoft gun, nobody has yet managed to use one in a violent crime or an assault. In our eyes this is based on the success of self-policing.

The above mentioned study was commissioned to ascertain at which point “lethality” was achieved in an airsoft gun firing BBs. The basic study found that this was at around 370fps although it did not test comprehensively and the definition of “lethal” is merely the level at which a BB may break the skin.

Presently, the law says that airsoft guns capable of firing beyond approximately 370fps on full auto or beyond approximately 520fps on single shot COULD be construed as Section 5 firearms. As yet we are not aware of any individuals who have been prosecuted for these offences in the UK and Government memos have indicate that the authorities do not wish to actively monitor the power output of imported guns or those owned by individuals. We still strongly discourage the modification of guns to fire at such high power levels as they will be largely unusable throughout the UK, in short, there’s no point so don’t do it, plus you could land yourself in prison!

About This Blog

Address: Just BB Guns, Trimex House, Pier Road, Feltham, TW14 0TW
Call: 0330 900 5224
E-mail: [email protected]
Blog Title: Get Started in Airsoft – Is Your Gun Within the Limits
Blog Author: Mark Watts

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