Airsoft guns are designed to shoot plastic spheres known as BBs (also known as airsoft pellets in some areas).
Although they are solid and are fairly hard to the touch, and while they may not be particularly pleasant to be hit by, airsoft BBs are pretty small, not very aerodynamic, lightweight (being made out of polystyrene or PLA plastic) and are designed to be non-lethal.
Airsoft gun BBs are what typically separates airsoft guns from other products in the airgun family, such as traditional BB guns and air rifles and pistols, and are what allow airsoft guns enthusiasts to shoot at one another in recreational and competitive games relatively safely.
BB sizes: 6mm Airsoft BBs Vs. 8mm Airsoft BBs
Generally speaking there are two sizes of airsoft BBs out there – 6mm and 8mm.
Most airsoft weapons use the 6mm size.
It is generally the standard most manufacturers adhere to across a wide range of airsoft guns, whether that’s machine guns, pistols, shotguns, rifles, SMGs, and so on.
If you aren’t sure what size BB an airsoft gun takes, it’s probably likely that it is designed for 6 mm BBs (although you really need to check, as we will discuss later).
In addition to 6 mm, there are some types of airsoft guns that are designed around 8 mm BBs, such as some sniper rifles (like some of the old Barretts), some pistols, some shotgun and more.
As you can imagine, these BBs are bigger and heavier than their 6mm counterpart, which gives them more energy to impart, makes them a little more realistic and allows them to be a little more stable in-flight.
It also makes them expensive, hard to chrono and means that they require slightly different internals (different diameter hop ups, inner barrels and so on).
Today, 8mm airsoft guns are pretty rare and can be hard to find outside of some specialty builds.
Further, there are relatively fewer examples and variants of 8mm BBs out there compared to their 6mm counterparts.
This can be disappointing to some players and can make them less useful on the whole and more expensive to buy and run.
What Happens If I Put The Wrong Type of BB in an Airsoft Gun?
There comes a point in every airsoft player’s life when they look at their gun, look at some small projectile and think “I wonder if this will work?”
Well, the short answer is don’t – it won’t work, it may damage your gun and it may even hurt someone.
Using Metal BBs
Don’t use metal BBs in an airsoft gun.
Even if they are the right size.
Aside from the fact that the higher density and vastly greater hardness of a metal BB can result in worse performance and cause catastrophic damage to an airsoft gun’s barrel, hop up and other internals, metal BBs are simply not designed to be fired at human beings and are extremely dangerous in an airsoft setting.
Metal BBs can cause severe injury to a person’s unprotected skin, eyes (easily causing blindness), teeth (to the point of shattering them), ears and other sensitive areas, particularly in the close ranges and velocities used in airsoft games.
Further, there is no airsoft gear out there that can offer adequate protection from this type of ammunition.
Using metal BBs in an airsoft game isn’t just dangerous and stupid, it will get you banned from airsoft sites, potentially sued and can easily lead to arrest and having some severe charges laid on you.
Using Larger Than Recommended BBs
As we’ve said, 6mm airsoft guns are designed to fit 6mm airsoft BBs.
Their inner barrels are about 6mm in diameter, their hop up units are designed to accommodate 6mm BBs, and the rest of their internals (gas system or AEG motor and gearbox) are designed to fire off BBs of a particular weight and density.
If you do try and feed larger BBs (like 8mm) through an airsoft rifle or pistol designed for smaller ammo, it will almost certainly jam and the heavier and chunkier BB may cause damage to the gun’s internals as it tries to pass through.
Using Smaller than Recommended BBs
Where things get interesting is when airsoft players decide to try and use smaller than average BBs in their airsoft guns, usually 4.5mm BBs.
Generally speaking, while these can work in theory, it’s not a good idea for a few reasons.
These smaller BBs tend to be denser and harder than their 6mm counterparts, which can mean that they won’t fit snugly in the barrel and hop up chamber.
As we’ve just mentioned, airsoft inner barrels are just over 6mm in diameter.
This allows 6mm BBs to fit snugly enough while still allowing a small cushion of air to build up around it and pass over its sides when fired.
A smaller diameter BB will likely still be pushed through the barrel when fired, but there will be enough space around it that it could start banging around the inside of the barrel, causing scratches and damage that can ruin a gun’s accuracy.
Further, due to the way hop ups work, using a smaller BB means you likely won’t get much spin on it as it leaves the chamber (as the nub wont press down on the passing BB quite as much), which will reduce accuracy and range.
Finally, because smaller BBs can be denser and harder than their 6mm counterparts, they can also present a danger to other players who aren’t expecting (or prepared) to be hit by them.
Airsoft BB Weight
As we’ve mentioned, airsoft BBs really only come in two sizes – 6mm and, far less commonly, 8mm.
An airsoft BB’s weight is a far more complicated subject than its size and they tend to come in three categories – lightweight, medium or midweight and heavyweight BBs.
Lightweight (0.12g – 20g BBs )
Lightweight BBs are a class of BBs that weigh between 0.12g and 20g.
Lightweights tend to be cheaper to run and it doesn’t take much to get them up to a high FPS.
As a result, they tend to be the favored weight for LPEGs, AEPs and spring-powered guns.
They also tend to hit their target faster than heavier bbs, which can be ideal for speedsoft, CQB and other fast-paced games and skirmishes.
On the downside, because they are so light they tend to be more affected by wind and air resistance, which can knock them off course and can cause issues with accuracy when played outside.
And while they may get to their destination more quickly, they tend to convey less force, which means that people may not notice their hits (or pretend not to anyway) a little more often, which is always annoying.
A final thing to consider is that very lightweight BBs, such as 0.12g, are usually hollow.
This means that, in addition to being more prone to losing accuracy with distance, they can deform, break or even shatter if used in high-powered airsoft guns.
Midweight BBs (0.20 gram BBs, .25 gram BBs & 0.28 gram BBs)
Midweight BBs range from 0.20 gram BBs to 0.28 gram BBs and, as the middle-of-the-road choice, they tend to be the most popular BBs used.
And this isn’t due to laziness or indecision.
Midweight BBs offer a good balance between velocity, impact force and accuracy.
Midweight BBs (particularly the 0.25 gram or 0.28 gram) can get up to speed pretty easily on a stock airsoft AEG or GBB gun and yet deliver a more noticeable impact when they get there than their lightweight cousins.
Further, while they may never be an ideal choice for snipers, they are heavy enough to stay more or less on course when fired, even when used outdoors.
Finally, while they aren’t quite as cheap as, say, 0.12g BBs, they also aren’t all that expensive and tend to have the most variants out there for players to check out.
As a result, midweight BBs tend to be the jack of all trades BB and, unless a player has some kind of reason to choose otherwise (say as a sniper), they are probably the best choice for day-to-day airsoft games and loadouts.
Their downside, of course, is that they are stuck between two worlds – they are a little more expensive and a little slower than lightweights and, compared to heavies, their impact is a little weaker and they tend to be blown around a bit more.
Heavyweights (0.30 gram BBs, 0.40 gram BBs and up)
Heavyweight BBs are usually those that weigh above 0.30g and are usually favored by long range shooters.
Their heavier weight means that these BBs tend to be less affected by wind and air resistance, giving them a more consistent and predictable velocity and trajectory compared to lighter BBs, which may be pushed off course or lose speed due to these effects.
Heavier BBs also tend to pack more energy and transfer more force to a target, which (personal amusement aside) can help ensure those wearing heavier clothing or other protective gear notice that they are being shot and call their hits properly…especially when fired at from long range.
It is for these reasons that heavier airsoft BBs are popular when used with DMR builds and with airsoft sniper rifles.
On the downside, heavier BBs are…well, heavier.
This means that they need more power from an airsoft gun to achieve a decent velocity compared to lighter options, which isn’t always possible to squeeze out of some guns.
Their increased weight also means that some guns’ hop ups can have a harder time giving them adequate spin, which can adversely affect their range, meaning they will have to be upgraded or even swapped completely to get things working correctly.
Different Airsoft BB Colors
Most airsoft BBs that you’ll see on the field or in stores are white or light-colored.
This can make them easy to see when loading (especially in lower light conditions) and makes them a little easier to track on their way to a target in most conditions, letting you better call your hits and check shot placement.
With that said, airsoft BBs can come in a wide variety of colors, such as black, yellow, orange, blue, green, red and more.
There can be a few reasons why players might want to use colored BBs.
Aside from making an airsoft game more fun, different colors can be used to represent different teams, which can help prevent friendly fire and make it easier to identify and track opponent hits.
For another, in low light and busy outdoor (such as when you’re near a lot of trees) certain bright colors, such as orange or yellow, can actually be a lot easier to spot than white,
Finally, the fact that some BB colors are actually hard to spot can actually work to an airsoft player’s benefit.
Should they want to be stealthy and not leave such an obvious trail for opponents to track, players can always use darker BBs (such as black or dark blue) to take advantage of low light.
BB Build Quality and Performance
While the vast majority of BBs out there should be fine for use, on occasion (and particularly when it comes to really cheap airsoft BBs) there can be a few flaws in their manufacturing process that can have a significant impact on performance.
A common, but not immediately noticeable, issue that airsoft BBs can have is the formation of air bubbles during their molding process.
These bubbles form on the inside of a BB and can make its density and weight far less consistent, which can cause them to fly more erratically and cause issues with accuracy and range.
Air bubbles can also weaken a BB structurally, making it more likely to shatter in your gun or on impact.
Another potential issue is in the molding process itself.
If a BB manufacturer doesn’t take care of or calibrate their machinery properly, the shape and size of its BBs can be inconsistent, which can lead to random jams or even damage to the internals of a gun in the worst case.
Finally, the use of cheap or low quality plastics can also be an issue.
Not only can cheap plastics be more likely to break or shatter, but they tend give BBs a host of quality control issues.
The use of cheap plastic can, for example, cause BBs to end up with far less consistent density and weight than they would otherwise, causing them to be less reliable and less accurate.
They also may not end up as well-polished as those made with more expensive plastics, ending up with a less smooth and more gritty feel that can increase their drag when fired.
For these reasons, when choosing BBs we feel its always important for airsoft players to look for higher quality BBs from well-known and reliable manufacturers, even if it can cost a little more.
Can or Should You Reuse Airsoft BBs?
Reusing airsoft BBs is a bad idea for a number of reasons, even if the BB itself doesn’t look like it has been flattened or damaged on impact.
Even BBs that look like they came out intact can have microscopic cracks or imperfections that can cause them to break or shatter inside the gun, potentially damaging its internals.
Should an airsoft BB shatter on its way out of the gun, it can become dangerous to those its being aimed at, effectively becoming plastic shrapnel that can damage property or other players, being capable of bypassing certain airsoft protection and tearing into their skin (or eyes).
Picking up a BB off the ground can also introduce dirt and debris into the hop up, magazine or barrel, which can cause the gun to jam or misfire.
Finally, reusing BBs is usually against the rules of most fields (for the aforementioned reasons) and doing so can cause you to get kicked out.
What Kinds of Specialty BBs Are Out There?
Glow In The Dark Airsoft BBs
Glow in the dark BBs, sometimes known as tracer BBs, are a type of airsoft BB that are specially designed for use in low light conditions.
These BBs are made of the same plastic material as other BBs (and can come in the same variety of colors and weights) but are coated with phosphorescent material that absorbs light when exposed to light.
When fired in a dark environment, this energy is released as bright, glowing, visible light of various colors.
All this allows users to better track their shots in low light conditions, something that can be particularly useful for marksmen in teamplay (for designating targets) and for those using machine guns (for walking their fire towards opponents).
It can also add a bit of realism to a night or twilight game, mimicking the effect of real steel tracer rounds, which can be really cool to see on a busy field.
On the downside, glow in the dark BBs tend to be more expensive than traditional BBs of the same weight, which can be an issue for those who need to buy them in bulk.
Further, these BBs tend to need an intense amount of light applied to them before they are fired, which generally means they need to be used alongside a tracer unit of some kind, adding to their cost.
Finally, of course, if you can see your BBs sailing towards an opponent, other players can certainly track them back to you, making you a greater target on the field.
Just as their name implies, biodegradable BBs are made of materials that are designed to decompose over time.
Traditional BBs are made of regular polystyrene or ABS plastics, and their use can contribute a great deal to local pollution due to the fact that they can take hundreds of years or more to break down.
Biodegradable BBs, on the other hand, typically break down within a few months to a couple years (depending on where they are left sitting), which can make them a more eco-friendly option than traditional BBs.
On the downside, a slight degradation of the PLA polymer these BBs are made of can affect their precision and performance on the field when taking long distance shots (to some degree), so they may not be able to be stored away in a closet after purchase quite as long as traditional BBs.
While the notion of reducing their environmental footprint may not appeal to some airsoft players, it is important to keep in mind that some fields and games (particularly outdoor ones) may require them in order to prevent long term soil contamination and to make clean up a little easier.
Whether it’s heavyweight BBs, glow in the dark BBs, biodegradable BBs or just a regular old BB from your local store, what your airsoft gun shoots can be surprisingly important on the field.
With small differences capable of affecting accuracy, range, power and overall performance, it is perhaps no surprise that there are a ton of choices out there.
As a result, in order to get the most out of your airsoft gun when it counts, it is important to take your time, assess your needs and pick the right BB for the job…even if it means occasionally spending a little more on small plastic balls.
Will Martin – Will has been into airsoft and paintball for well over 10 years, and has done it all – from upgrading and fixing gearboxes as a tech to building custom airsoft loadouts for his friends to supporting off those friends as a DM.