Lazs, at the time the Bill of Rights was written virtually every able bodied man in the Colonies was in a "Militia." There were no meetings or drills, but whenever the church bell gave the alarm everyone grabbed their gun and assembled.
Personally I believe gun ownership at that time was thought to be such a basic right- actually a basic necessity of life- the Framers didn't feel it was worthy of guarantee, any more than giving you the right to wear a hat was mentioned. What WAS worthy of mention was the right of citizens to band together to protect themselves against the tyrany of even their own Government, which was a novel idea, and is what the Second did.
If I were to advocate for gun ownership I'd point out the customs of those times allowed everybody to own and carry the most advanced weapons of the day, and was never intended to be resticted at any rate; I'd imagine the Framers would be spinning in their graves if the Citizens here were told today we can no longer own firearms.
So in my humble opinion the Second states we have a collective right to form militas rather than an individual right to own guns because the individual right to posess a gun was such a universal necessity of life during those times, like posessing a plow or an axe.