What are the limits of the second amendment?
"Shall not be infringed" sums it up about as clearly and concisely as is humanly possible.
the part about the well regulated milita is not considered to be
necessary today
"Being necessary to the security of a free state" is a timeless statement, notwithstanding the gullibility of some modern folk. A well-regulated militia is a Constitutional mandate. By definition, we are not living in a free state if we do not fully maintain said well-regulated militia.
Also by definition, said militia is not to be a standing army, but rather is defined in US Federal Code as
"all able-bodied males at least 17 years of age and, except as
provided in section 313 of title 32, under 45 years of age who are, or
who have made a declaration of intention to become, citizens of the
United States"
This is the mechanism by which the security of a free state is ensured. The Second Amendment is unambiguous about both the purpose and extent of this right.
the second amendment guarantees a right to gun ownership for
self-defense.
Correct, although this also extends to mutual defense.
But there are limits on gun ownership today, so I don't see where
exactly the line is on regulation that is allowed by the second
amendement and which kind of regulations would violate the second
amendment.
All such regulations violate the Second Amendment. "Shall not be infringed" is quite express. Any and all arms that serve the end of securing a free state cannot constitutionally be limited or regulated in any way. Any such regulation would by very nature limit the freedom of the Authorized Militia of the United States to perform their proper function, and constitute an infringement.
However, we must acknowledge that we live in a society that presently tolerates various unconstitutional edicts and practices. In effect, there are two different governments in America today. Just because we have a Constitution doesn't mean that our elected officials or appointees actually uphold or enforce it. Presently, conflicts abound between the Constitution and contrary rulings advanced by various legislatures, judges, officers and executives. The existence or absence of such a discrepancy in written policy does not guarantee that justice will be done, nor that rights will be properly upheld, nor that punishment will not be inflicted. Each person is advised that he is responsible for knowing local, state and federal laws and regulations and may be subject to punishment by unhinged agencies that do not regard the Constitution as the Supreme Law of the land, or who "interpret" citizens' rights out of existence, or if while ostensibly exercising a legitimate Constitutional right, an individual violates a different law that is constitutional and the transgression of which is therefore punishable. I am not a lawyer.
The only reason there is any debate on the subject is that there are people who want this Amendment and guaranteed right not to exist, or who wish to undermine it and control the people in significant, unconstitutional ways.
But the Second Amendment is very clear.
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.