In my opinion, second amendment provides, in line with the times in which it was written, to allow the individual to bear arms. I do not believe that any of the founding fathers thought for a moment that it should be okay to possess a fully automatic machine gun privately. I also believe the right to bear arms was enacted for personal protection and hunting purposes, as the lifestyle back then would demand.
They didn't think about it, because they didn't exist yet.
But militias used cannons, the equivalent of modern day artillery, and you can bet the founders intended the second amendment to protect cannons.
Beyond the question of modern weapons developments, the founders clearly intended for the citizenry to have whatever sufficient firepower would be needed to oppose and dominate ANY illegitimate threat to liberty, whatever that threat may entail.
If the only weapons that are available to the citizens are insufficient to oppose those illegitimate threats to liberty, then the amendment will have been gutted for all practical purposes.
Remember a militia is primarily a military unit of the state. The founders intended for the militia to be regulated. I think is reasonable to highly regulate the possession of cannons (artillery) and fully automatic weapons. The more powerful the weapon, the more it should be regulated. But regulations must have a basis that is connected and drawn from the intent and purpose of the amendment. Regulations can't be onerous, or designed to suppress the right. They must support the intent of the amendment.
In my opinion, highly regulating fully automatic guns is fine. Requiring training for safety, proper use and marksmanship all serve the interest of the state (i.e. the people). Background checks on individuals who wish to possess them; safe and secure storage requirements are all fine.
What the founders clearly intended to be OFF the table is entirely banning access to weapons.
Leaving NO available path to owning them would be a ban and therefore it is unconstitutional, IMO.