2nd Amendment and "original intent"

I'm not a lawyer or a Constitutional scholar, so what follows are just the ruminations of a citizen who pays attention.

Second Amendment to the Constitution
(one of the first 10 Amendments, known collectively as the Bill of Rights.):

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.

The book from which I learned about the United States Constitution, in 8th-grade civics, is Your Rugged Constitution by Bruce & Esther Findlay. Once out of print, it is now available in a 2014 hardcover edition from Amazon.
In their commentary the authors explain:

You deny: To the federal government the power to interfere with your ownership and use of weapons for lawful purposes.
You get: Protection against the wrong use of power by a national army.

Okay, here goes.

One school of Constitutional interpretation is "original intent": What did the Framers MEAN by the words they wrote?

For the moment I'll ignore that devilish introductory clause about a "well regulated militia".

When the Framers wrote "arms", what did they mean?
The only personal arms known to them were smooth-bore and rifled, muzzle-loaded flintlocks - both long-guns and pistols.
They also knew about smooth-bore and rifled, muzzle-loaded field artillery.
They did NOT know anything of breech-loaded weapons, or percussion caps, or revolvers, or automatic weapons of any sort.
They did NOT know anything of tanks, or rocket-propelled grenades.

Should we, by the interpretive doctrine of "original intent", constrain "arms" to mean only muzzle-loaded, single-shot weapons?
After all, how could the Framers have intended AK-47s, M16s, ... or even 45-caliber automatic pistols?
They had never seen or imagined any of these.
How could they "intend" these in any meaningful sense?
They were not writing science fiction.

Okay - so THAT is much too narrow an approach to "original intent".

Uppermost in the Framers' minds was the recent conflict with the tyrannical government of George III. (A conflict that they WON! - thanks to "citizen soldiers" and militias.)
Perhaps what they intended was that citizen-soldiers be equipped to fight against a tyrannical central government - whether foreign or domestic.
In this case, "original intent" would seem to imply that the potential citizen-soldier ought be allowed to "keep and bear" any arms which that hypothetical tyrannical central government possessed.
Today those permitted arms would include assault rifles, machine guns, grenade launchers, ... and tanks, fighter aircraft, drones, ... well, you get the idea.

Is THIS the correct interpretation according the doctrine of "original intent"?
I should be able to wander into my neighborhood gun store (yes, there is one) and buy a 50-caliber machine gun?
A rocket-propelled grenade launcher?
An M1 Abrams tank?
Without such weapons, how can I possibly hope to confront, let alone defeat, a tyrannical federal government?

I note that each of these would be GREAT for purely self-defense purposes!
You know, my home is my castle, and I'm going to defend it, goddammit!

One of my loyal readers has suggested that there is an implied limitation based on that horrid "well regulated militia" clause. I quote his comment in full:

The argument I heard is that the arms which the 2nd Amendment protects are arms which a militia might carry and use. AR-15 rifle? Yes. Hand grenade? Yes. Tank? No. Heavy artillery? No. Mortar? Yes if light, no if heavy. RPG? Yes. Davy Crockett tactical nuclear recoilless rifle? Hmmm.

What I REALLY want is for someone to pose this question to the GOP candidates:

What, if any, restrictions ought be placed on my right to "keep and bear arms"?