should be guns that exists in 1791 and only if you are in a well-regulated militia.
You are a member of the well regulated militia envisioned by the constitution. Everyone is.
If you're talking about a government-organized entity, you are not talking about the militia. You are talking about an "Army" or a "Navy".
Congress has the power to determine what part of the militia can be called forth, and the circumstances under which they can be. Under that authority, they enacted 10 USC § 246 which basically says they intend to call the National Guard first, and if necessary, able bodied male citizens ages 17 to 45.
They don't define the constitutional meaning of "Militia" when they create the two classes mentioned in this law. They could change the requirement from "citizen" to "person subject to US law" or "able bodied" to "sound minded", or "male" to "person", or "17-45" to "16-60".
The largest group they could theoretically draw is the entirety of "We The People", and that is what the Constitution means when it refers to the Militia in Article I Section 8 clauses 15 and 16, as well as the 2nd Amendment.
When called to serve, as the National Guard is called today and the unorganized militia was called in Vietnam, Korea, WWII, WWI, and many, many other wars, individuals are not called forth to the militia. They are called forth from the militia, to serve in "armies" or the "Navy".
The only regulation most of us ever see is an obligation to register for Selective Service. If you don't think that the militia you are a part of is sufficiently regulated, I want to know what additional regulations you feel you need imposed upon you.
You don't get to make those additional regulations conditions of gun ownership, as that would violate the 2nd amendment. But you can impose additional training requirements on yourself and the rest of We The People. You could obligate every high school student in the nation to take a class on safe gun handling and the laws governing use of force, for example.