They came out in 2002 as my wife was one of the first ones. You did not say which one you had.
The first rounds were Hornady, and they use a 17gr bullet that is modeled after their varmit bullets. When they hit something they rapidly expand and fragment inflicting a considerable amount of damage. The tip also helps with the BC. Of course there are others that make them now, and some are HP types. My wife still shoots the regular Hornady load. Find one that you like, and your rifle likes, and once sighted in get a bunch. They all shoot slightly different, and if you want to make those 200yd+ shots, you need to be using the same bullet as you are sighted in for.
We like it better than the .22 mag since it shoots farther, flatter, has a better bullet, and isn't as prone to ricochet.