Mainly to answer overloads question. Generally a " carbine" is a shorter lighter version of a standard rifle, bolt action, semi-auto, lever gun,pump, even single shot. Some exceptions have occurred, the M1 carbine is a rifle unto itself, it is not a scaled down M1 garand, shoots neither rifle or pistol caliber at the time, it was brand new and sort of breached the gap. The carbine initially was developed for calvary and then later for close quarters, like tanks, jungles and trenches. In modern terms cars, and entry ways. It can be rifle or pistol calibers certainly. I have several carbines and they are definitely the most fun to carry, and in some instances shoot.
To MB: GREAT ARTICLE, I'm glad it was published. The reviews and comments speak for themselves, the AR15, not just for breakfast anymore. I'm in the automotive business and we have a saying, no matter what vehicle you choose, you are always driving your tires. In this case, your always driving your caliber, it will perform to certain limits, learn them, experiment with them, then use them. However I prescribe to the old " main battle rifle " theory. A battle rifle should penetrate a standard helmet at 800 meters. Any thing less is not a battle rifle. I won't use the other term. I own and use them all, I just won't put the 5.56 or the 7.62x29 in a catagory it does not belong. Valid yes, the ultimate no. Fun, oh hell yes!!!