The 17 grain ballistic tip bullets are more frangible than the 20 grain hp’s. For example, if a 17 grain bt bullet strikes a bone in a small animal such a squirrel for example, the bullet will break up and turn the inside into mush. The 20 grain .17 hp’s will punch through without having the same effect. The 20 grain hp’s have greater penetration, the 17 grain, more explosive on impact. They can make a real mess of rabbits if you intend to eat them, you’ll need to head shoot them.