not sure if this is the right place, but I assume someone will see it here and know the answer for me. I've always been a bit fuzzy on the rules between a rifle and a pistol, meaning, in the eyes of the law, what's the difference, and what's legal? for example, lets say you have an AR-15 platform. the lower is marked in a rifle caliber, ".223 / 5.56" an 18 year old can buy it because it's a rifle. but because it's a rifle, it cannot have a barrel shorter than 16" and the overall length has to be 26" correct? now, I see 14" and shorter AR barrels, and I've heard about "Short Barreled Rifles" which are only available to LEO/Military -- if you get a class 3 stamp, I assume you can buy one as a civilian? but, I've heard about pistol ARs Is it possible to get an AR lower recieiver that's a "pistol" in the eyes of the law, you have to be 21 to buy it, and then you can legally put a 14" barrel onto it? As far as the law goes, what makes a "pistol" with a 6" barrel ok, but a "rifle" with a 10" barrel illegal? is it the caliber? does the federal law recognize certain calibers as being rifle only or pistol only? how does that work with say, a .22? or a 9mm carbine?