Everything you need to know about airsoft BBs
By B.B. Pelletier
Airsoft guns (or soft air or whatever else they may be called) owe a large part of their "soft" performance to the ammunition they shoot - 6 millimeter balls that the industry now calls "BBs." They're not the same as steel BBs used by conventional BB guns. Airsoft BBs are usually plastic and sold and used according to their weight.
Grams vs. grains
The weight for an airsoft BB is listed as a fraction of a gram rather than a grain weight, which is how airgun pellets are stated. There are 7,000 grains in a pound, but only 454 grams in the same pound. Therefore, one gram weighs about 15.43 grains.
Airsoft BB weights are stated as a fraction of a gram. The lightest is 0.12 grams, and then the weights jump to 0.20 grams, 0.25 grams and so on. All these different weight BBs are the same 6mm size, so the varying weights come from different compositions.
Increase your fun with aluminum, biodegradable & tracer BBs
Some airsoft BBs are made of aluminum and are very heavy, others are environmentally friendly and biodegradable, and still others glow in the dark and create a realistic tracer effect when shot at night. Several companies are developing airsoft paintball BBs, though the technology is not quite where it needs to be for reliable operation in automatic electric guns (AEGs) or reliable breakage on target.
The lightest BBs are used in inexpensive spring guns such as the Daisy Airstrike 240, which shoots at a lower velocity. The 0.20-gram BB can be used in gas guns, such as the M9 Tactical Master, and more powerful electric guns, such as the DPMS Panther A-15. In fact, 0.20-gram BBs may be the most common weight used. That said, there are still plenty of guns that shoot best with other weight BBs. Check the gun's box and owner's manual to find the right weight BB.
Why Hop Up increases accuracy
Most airsoft guns have some sort of Hop Up mechanism to assist with accuracy. Hop Up imparts a backspin on the BB as it leaves the gun. Without it, BBs fly erratically; with it, they fly relatively straight and do not fall quickly. In the more expensive guns, Hop Up is often adjustable, so you can experiment with several BB weights.
If you use the wrong weight BB in a gun that can't be adjusted, it will not be nearly as accurate as it would with the right one. Read the instructions and don't improvise unless you have an adjustable gun.