Which BB is chosen depends largely on personal preference and experience, but we can still offer you some sound advice that’ll help you in the right direction. It’s common practice to use the same BBs in both your airsoft rifle and your airsoft pistol. The reason is simple; you only need to carry one bottle of BBs and one speed loader. That saves weight and space, prevents mixing things up and will gain you precious time.
For airsoft rifles and pistols a 0.25 grams BB will be a good starting point. Slower than a lighter BB, but with a flatter trajectory and less sensitivity to wind, resulting in better accuracy. When there’s more wind, you can choose a heavier BB and vice versa. Of course, the power of your airsoft replica will have a large impact as a powerful replica will fire heavier BBs with more speed than a less powerful one.
Airsoft snipers are very powerful, because they have to shoot longer distances, which means heavy BBs are used. Mostly a sniper won’t go lighter than 0.36 grams and an often used base weight is 0.40 grams.
The use of white or bright coloured BBs has the advantage the BBs can be followed with the naked eye, making it much easier to hit your target. Dark coloured BB’s won’t have this advantage, but they are often used by airsoft snipers as -though aiming will be more difficult- they won’t betray the shooters' position. When shooting in the dark, tracer BBs can be interesting. They feature a fluorescent layer that will glow in the dark after being shot through a tracer-unit which illuminates the BB with UV light. These BBs will then light up as tracer ammunition. You can use them as they are or mix them with your normal daytime BBs.
Its advisable to use polished BBs with a high density. Cheap, rough BBs can have edges and not be truly round. This will accelerate wear of your replica and accuracy will be less too. They can also be brittle, making them more prone to fragmenting which -when that happens inside your replica- can cause defects.