The 2A has two clauses. The right to keep arms and the right to bear arms.
The right to bear arms is quite clearly "render military service" or "militia duty". In other words, the right to use arms in the militia (as stated in the the US Constitution)
Amendment II: House of Representatives, Amendments to the Constitution
In this document they're discussing this clause "but no person religiously scrupulous shall be compelled to bear arms.""
Mr Gerry (of gerrymandering fame) said "Now, I am apprehensive, sir, that this clause would give an opportunity to the people in power to destroy the constitution itself. They can declare who are those religiously scrupulous, and prevent them from bearing arms."
Okay, so, Mr Gerry was worried that people stop having the right to carry arms which would destroy the constitution, or he was worried that people stop having the right to be in the militia which would destroy the constitution?
Well, he very next words were "What, sir, is the use of a militia?" Kind of clear that he's talking about making sure the militia doesn't get destroyed by the Federal Government.
Mr Gerry also said "Now, if we give a discretionary power to exclude those from militia duty who have religious scruples, we may as well make no provision on this head."
Pretty clear that Mr Gerry thought that "bear arms" meant "militia duty"
"Mr. Jackson was willing to accommodate. He thought the expression was, "No one, religiously scrupulous of bearing arms, shall be compelled to render military service, in person, upon paying an equivalent.""
Mr Jackson thought that "bear arms" meant "render military service.
It's quite clear that the Second Amendment is about the militia. It says so in the Second Amendment. The first words are "A well regulated militia", the whole point of this militia is "being the best security of a free state".
So, the right to keep arms is the right of individuals to own weapons, weapons the US Federal Government cannot just take when they call state militias up into federal service.
The right to bear arms is the right to militia duty. Because if the US Federal Government could ban individuals from being in militia, then the militia would have guns, but no personnel, and therefore useless.