The airgun pellet is a curious little projectile. Unlike BBs, a pellet is not round and unlike a bullet that is fired from a firearm, the pellet is shaped differently still. The base design of all airgun pellets is as such. The pellets major components of a pellet are the head, the waist, and the skirt.
The head is made to a critical dimension. It is just smaller than the bore of the rifle's barrel. The waist functions as a division between the head and the skirt. The diameter of the waist might vary with the weight of the pellet with heavier pellets utilizing this area to add mass to the pellet.
Next you will find the skirt of the pellet. The skirt looks exactly like you would expect it. It is a flared area of thinner lead (or alloy) that will balloon slightly when air from the shot tank or compression chamber hits it. This slight expansion of the skirt allows for the pellet to engage the rifling of the barrel to create a stable, accurate shot.
Since the head and skirt are initially smaller than the barrel, loading the pellet into the barrel or magazine is super easy.
The basic design is very common across the various pellet manufacturers, the head shape can vary quite a bit. Most people are very familiar with the standard flat tipped pellet.
Flat tipped pellets are great for use in target shooting as they make a nice clean cut through the paper target. The downside of flat tipped pellets is they are typically much lighter than other pellet designs. As such, flat tipped pellets are best used at closer distances (under 25 yards).
The most popular pellet shape is the dome head. Domed pellets can be heavier than flat tipped pellets and can fly true at longer distances. Airgunners commonly shoot domed pellets at distances beyond 100 yards. Domed pellets can be used for plinking, target shooting, or hunting.
Pointed pellets are good for use in situations where maximum penetration is required. Pointed pellets tend to be a bit heavier than flat tipped pellets but will peak in weight below the domed pellets.
Hollow Point Pellets claim to offer excellent performance when hunting. However, due to the physics of airguns, you may or may not see any expansion that hollow point firearm projectiles are known for.
These are the most common pellet shapes on the market. In general, you should always prefer a pellet that gives you the best accuracy in your gun regardless of shape.