THE MOST IMPORTANT FACTOR for good airgun accuracy is the ammunition. It doesn't matter how good or expensive a weapon you have, if you load it with the wrong diabolos, accuracy will always suffer. It is at least as important for simpler air weapons. If you find the right shape, size and weight of your ammunition, the mediocre hit pattern will be radically reduced.
We* solve 9 out of 10 cases of accuracy problems with airguns, just by changing ammunition - in most cases to someone from JSB. JSB is one of the world's leading manufacturers of diabolos for air weapons. Most people who compete in one of the long-distance disciplines today use some model from the Czech manufacturer. During the Field Target World Championship in Italy in 2011, more than 90% of the competitors used JSB ammunition!
The secret lies in the quality of both materials and manufacturing process. High knowledge and a unique design with several different weights and sizes means that you can precisely match the diabolo to the barrel. JSB specifies exact measurements of its diabolos (applies to the "head"). For example. 4.49mm, 4.51mm and 4.52mm are all diabolos for 4.5mm (.177) caliber weapons. All barrels are different sizes, but most barrels seem to prefer a diabolo slightly larger than the stated caliber. 4.52mm and 5.52mm are the most popular sizes.