Re: I'm a young buyer looking into buying a decent semi-automatic rifle.
What you buy depends on what the intended use is. A large caliber rifle is not the right choice for home defense for several reasons - one being penetration thru walls into your neighbors home. Semi auto's for hunting can have their uses however, but I'd look at something besides a black gun for that purpose. For home defense, a DA revolver .38special or larger, or short barrel pump shotgun loaded with #2 birdshot or #4buckshot would be ideal. Keep in mind that home defense is close quarters, you'd likely be in the process of waking up, in the dark, and confused. You have a couple of seconds to react if you're lucky. You really want to mess around with jacking a round into the chamber?
I have a 5 shot S&W .357/.38 with 3" barrel for bedside use. All I have to do is pick it up and start pulling the trigger. At 20' or less, I garuntee at least 2 of those bullets will hit the target, even half asleep and in the dark.
That said, don't rely on a single thing. Defense in depth. I have other security that will alert me well in advance of an actual breakin.