Earlier quoted context omitted.
IANAL but I’m pretty sure the second amendment only applies to guns; you can’t walk around with an RPG on your shoulder.
How it's written I personally think you should be able to buy any weapon available on the open market. Or at least any weapon that could realistically be used by an infantryman (as the wording is "A well regulated Militia, being necessary to the security of a free State,." I'd rather have a new amendment then have judges be able to decide what the definition of arms is. Slippery slope. They really could one day decid…
U.S. v. Miller loosely established the test (later solidified in 2008's Heller v DC) that weapons commonly used in militia service are inherently deserving of second amendment protections.
Miller, a known mobster who was caught with a sawed off shotgun lost his case because
a) the military testified that they had never used sawed off shotguns, so they were not useful to a military, ergo a militia (which was a lie -- they had used them, and found them useful for trench-clearing)
b) Miller's attorney was not very good, and didn't even challenge that testimony, much less so by totally disproving it -- I offer a little sympathy here as they didn't have Google at the time
Also noteworthy, Miller was actually dead when the decision came down, as he'd been murdered, and because /shrug, the trial kept going, but the defense (for obvious reasons) quit trying. He was sentenced in absentia.