BB's are a common name for Airsoft Gun ammunition, but are a misnomer, with the name derived from .177 caliber BB's, a totally different ammo.
The defining characteristic of BB's to airsoft performance is that they have different weights to them for different characteristics.
-The lighter your BB, the faster your FPS. Lighter BB's also tend to be less accurate and have less range thanks to decreased inertia. -The heavier the BB, the slower your FPS. Heavier BB's tend to be very accurate and have more range thanks to the mechanics of hop-up.
Commercial BB weights
.12 gram: These are the lightest and cheapest BB's commercially available. While they do give a higher FPS and require less energy to move, they lose range (and FPS) quickly and are very easily shifted off course by wind.
.20 gram: These are the most common and most used BB weight. Many if not all Airsoft fields chronograph using .2 gram BB's. Performance is highly desirable, with a relatively high FPS and inertia.
.23 to .25 gram: Just slightly heavier than .2 gram BB. Heavier BB yields more range and accuracy.
.27 to .40 gram: Heavy BB's for use in High-FPS airsoft guns, especially sniper rifles. Usually highly accurate and retain their FPS over longer distances.
What BB's to choose
This is a reference chart for choosing which BB's to use, But the best way to choose is to take different BB weights and try them yourself. Also, contrary to popular belief, the use of light BB's in a high-power airsoft gun will not damage your gun. It will only affect performance.
0.12g: >280 fps 0.20g: 240-370 fps 0.23g: 330-430 fps 0.25g: 350-480 fps 0.28g: 390-500 fps 0.30g: 400-600 fps 0.40g: 450< fps
Use of low-quality and price BB's will only hurt you in the long run. Here are some things to watch out for as clear indicators of bad BB's. -Brightly colored in unusual colors (neon green, blue, sometimes yellow) -Clear/translucent BB's -BB's with seams in them (seams typically run along the center line and are proof of low quality manufacture) -BB's notorious for being very low-quality (e.g. Crosman or Chinese BB's) -BB's that are not perfectly round (I.e. don't even look like BB's) -BB's with highly varying weights from the same package (you can chronograph and/or electronically scale to check).
Apart from conventional BB's, there do exist multiple other types of BB for use in airsoft.
- Biodegradable: Commonly abbreviated as "bio", biodegradable BB's are not as polluting to the environment as regular petroleum-based BB's are. Required by some fields as a standard BB type.
- Tracer: These special BB's are coated with a special substance that will cause the BB to glow when exposed to a certain light. Often used for nighttime operation for better shot tracking.
- Paintball: Special 6mm marker BB's. The thin shells of these tend to break very easily, especially in guns with hop-up or high capacity magazines. For target shooting only, use at own risk!