How do I find the right pellet for my gun?

Buy a sample pack or three or four tins of different brands, weights, and head shapes (domed is the right starting place).

Shoot 5- or 10-shot groups at a representative distance (25 yards is a good benchmark) using identical hold and rest. The pellet that produces the smallest group consistently is your gun's pellet, full stop. Do not trust online forums; barrels vary even within the same model. Plan to spend an afternoon and a few hundred pellets on this; it is the single highest-leverage thing you can do for accuracy.