Let's put aside all the emotionalism and look at the 2nd amendment in the raw, cold light of logic alone.
If you want to know what the 2nd amendment means you have to understand the times in which it was written and the 'shape of the world' then. It is impossible to understand The Constitution or the Bill of Rights without an appreciation of The Declaration of Independence. In computer parlance, The Constitution is the Users' Manual and The Declaration of Independence is the specification document. Can't understand something in the users' manual? Go back to 'the spec' and find out what was intended.
Now, of all the parts of the Constitution, possibly the most confusing is the 2nd amendment: "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
To understand what the 2nd amendment means we look into the Declaration and we find this: "...to secure these rights, Governments are instituted among Men...", and a little further along: "...whenever any Form of Government becomes destructive of these ends (i.e.: 'securing these rights'), it is the Right of the People to alter or to abolish it...". Government exists to seecure our rights, and when it doesn't do that we have the right to abolish that government, but how?
A government which has turned from 'securing these rights' to 'removing these rights' is not going to be swayed by any 'petition for a redress of grievances'. King George III wasn't, and that's why we had a six-year war with the finest field army Europe had produced thus far.
That's where the 2nd amendment comes in. The purpose of the 2nd amendment is to allow we the people to overthrow our own government by force if necessary. With that in mind, what might "reasonable restrictions on guns" look like? What fool would allow any government to "reasonably restrict" the guns which might one day be used in its violent overthrow?
The British lost the American Revolution to some extent because the weapons the colonists had, Kentucky long rifles, were better than the Brown Bess muskets the British troops carried. Remember that the next time some moron tells you that the M-16 is a 'weapon of war' and shouldn't be available to civilians.