A frightening article in this week's New York Times magazine section (called to my attention by Dave Krinsky) discusses the easy availability of .50-caliber rifles. Although a .50 can hurl a six-inch bullet several miles with enough momentum to go through a three-inch thick manhole cover, you can get one with no more fuss than for any rifle purchase, and once you have it, no governmental records are kept to track it.
I don't go in much for teleology, but this is a case where the argument from design holds together, I think. The telos of a firearm is to shoot at things, and the .50 distinguishes itself by being useful only for shooting at big, well-armored, and slow-moving things. The telos of a .50-caliber rifle is to fight against an army, one with tanks and fortifications. At 37 pounds and 54 inches, it's actually not much of a weapon of mass violence or indiscriminate terror. You don't pull out the .50 in a domestic dispute, you don't take your .50 when you go shoot up an office building. You need your .50 when they come for you with the black helicopters and the armored personnel carriers.
The .50-caliber rifle puts Second Amendment issues in a particularly harsh and merciless light, I think. The impracticality of the .50 means that it is useful only for those purposes firearms-rights advocates constantly trumpet: to secure the bearer against an invading and well-equipped force (of the sort that only governments and major mercenary organizations can muster), or for the pure recreational thrill of going out in the desert and shooting up rocks and old junk. It's a bit ironic that the most powerful weapon available today is the one most immune to standard gun-control arguments, but any debate over the legality and uses of the .50-caliber rifle really does come down to the question of whether you think individual citizens should have the firepower to effectively and violently resist the government.
That is to say, having thought a bit about the .50 and its dangers, I've realized that I am a genuine anti-purist when it comes to the Second Amendment. I don't want .50-caliber rifles in the hands of Joe Public, because I really do sleep better at night knowing that Joe Public can't take his county in Idaho out from under the jurisdiction of the United States in America. This is a measure of patriotism for me: I trust this country, in the large, and I trust it and its institutions not to engage in wholescale oppression of the sort that is the subject of paranoid fantasies. Several hundred years of history have told me that in a conflect between the Feds and the locals, it's usually the Feds who are in the right. There are two good reasons why the US didn't devolve into the "Election Mayhem" described by The Onion. First, we have a well-established political process and a well-established national culutre of peaceful transfers of power and legal resolution of disputes. And second, when the National Guard gets called out, order gets restored -- and people know it, which is one major reason why the National Guard doesn't get called out all that often.
Put it this way: I'm not afraid of .50-caliber rifles; I'm afraid of what the people who own them might do with them. Guns don't stage heavily-armed insurrections, people do.