Initially These United States were not called The United States. Each State Was a soverign entity; each had its own army.
You can quibble about meanings, but the definitions I gave you are from an English Dictionary printed about 1814 (Geo III's son had just taken over as Regent), and not just my opinion. The founders spoke and wrote in English, unchanged from the mother tongue, rather unlike today's American version.
More research leads one to discover that there were many different wordings considered to express this fundamental right, but the understanding that an opressive, largely military government had been so recently thrown off made explanation unnecessary.
Who would have thought that our culture (not human nature, but our culture) might evolve to the point that the right to arms and even self defense would be questioned?
There are still a number of opressive and tyrannical regimes in the world, and the only thing necessary for it to happen here is for people to lay down their arms and say it cannot.
The infantry firearms of the day were muskets used in volley (area) fire.
One of the prime strengths of the Colonials was that they were not trained in "modern" infantry tactics, nor were all using the same weapons.
Rather, the Colonists used hunting arms, including rifled weapons, capable of more accurate fire, with occasionally devastating results.
Sharpshooters aimed at the enemy's commanding officers, not just the rank and file as was the European custom.
The Iroquois (and others) had taught many (by experience) the advantages of the skulking way of war, using cover and concealment to gain advantage on the enemy.
Had they been trained in infantry tactics of the day with common infantry weapons of the era, they would not have had the advantages provided by unorthodoxy.