.223 round
.223 bolt gun is extremely accurate.
This depends on the rifle barrel, headspace distance, and a billion other factors. rounds in and of themselves tend to have a greater affinity towards certian amounts of accuracy, but the rifle and the shooter are of fundamental importance...
the walmart test is a great one, I guess I have kind of used it with out identifing it. if you dont have a shooters supply close that sells cheap ammo, walmart is the best bet.
lotts of reasons
there are so many reasons people own firearms. history, shooting for fun, personal protection, hunting... I tend to own them because of their value (investment) hunting and its a great hobby to get into if you like technical stuff like reloading.