The 22 rimfire has long been a favorite of the poacher. This should answer the question of stopping power. If you have the time, get many different brands of ammo, hollow point and solid. Your rifle or pistol will favor one or maybe two. These are the ones to use. The CCI Small Game bullet has proven to have very consistent velocity. This is a key to accuracy. Your standard velocity ammo is generally more accurate than others, and for defense purposes your hyper velocity or fragmentation rounds might be the best bet. But again, all the speed in the world is useless though if you can't hit the target.