So much wrong in this post...
it's telling that one of the only types of gun that have been nationally restricted are automatic weapons. Despite the fact it's commonly called the "Assault weapons ban", that's about as laughable as the name "Patriot act".
AWB has expired years ago, but even when it was there, it had absolutely nothing to do with automatic weapons. Those have been regulated by NFA, GCA, and FOPA.
Although there are sometimes full-auto weapons used in military assaults, the majority of US Army soldiers only carry single and burst-fire rifles (excepting special forces). Full-auto weapons haven't been standard issue since early-Vietnam when it was realized full-auto is just a waste of ammunition in most combat scenarios.
The standard infantry weapon of US Army today is M4A1 carbine, which has two firing modes: single shot, and full auto (they are not fully converted from M4 yet, but they're working on it). The reason cited for this is that experience in Afghanistan has showed that full auto is a necessity.
Also, US military has been the only one in the world that restricted its infantry weapons chambered in intermediary cartridges to three-round burst; everyone else who introduced such weapons enabled full auto for them (sometimes also having a three-round burst mode, more often not). So US is rather catching up on that front, after several decades of stupidity that was originally introduced in M16A2 design-by-[USMC]-committee process, because they took their "one shot - one kill" mantra a bit too serious. Army protested back then, but they were ignored largely for fiscal reasons.
The problem that he is trying to address, I think, is that buying it from a dealer leaves a record. First there's the NICS check - and yes, by law those are transient and remain in the system for a few days only, but I would be very surprised if NSA doesn't get to stash it somewhere in practice. Then there's the 4473 form that's filled in for that check to be performed, and that the dealer has to keep around basically forever. While the government doesn't get the form - which allows them to say that they do not maintain any kind of gun registry - in practice ATF can come to any licensed dealer and demand them to turn over all their 4473s, with no reason or explanation necessary. So in practice it's a kind of registry, just a distributed one, and it makes some libertarian-minded people uneasy.
I'm no expert, but it seems to me that making a barrel is the hardest part.
Making a rifled barrel is. But a shotgun barrel is basically just a pipe of the right diameter, and it doesn't even have to be particularly strong - the pressures are low enough.
Correct me if I'm wrong, but doesn't AR require only a full auto sear and a corresponding bolt to make a semi-auto one into a full auto? so the receiver itself (which is the serialized part) doesn't really matter, only the bits which are housed inside it (and which are not controlled).
In any case, they track things separately for NFA purposes. For example, a full auto sear is a "machine gun".
I'm not sure why this is a big deal, its still REALLY hard to build a barrel and chamber so you still need to buy them, honestly making the receiver the registered part is silly most people could build a receiver with time and effort few people could make a decent barrel or precise chamber.
Building a rifled barrel is hard. A smoothbore is fairly easy, though, and it's still "accurate enough" out to 100 yards or so (on human sized targets, anyway). In a close range full auto firearm, you care even less about accuracy.
And turns out that you don't even need to build it - you can just take some standard pipes and use them for it. There are some that fit remarkably well for 9x19mm, for example, and a guy in UK built a submachine gun out of them, and wrote a book about it. That being UK, the guy is now in prison, but the book is still on Amazon.
What about all deaths?
Actually, let me answer that for you: they did not. The drop in gun deaths was largely from gun suicides, but the overall number of suicides did not decrease with the ban, it's just that the preferred method changed (to hanging, for some weird reason).
And yes, both deaths and suicides have slowly decreased overall since then - at the same rate at which they were decreasing before the ban.
So, basically, the takeaway from the Australian experiment is that banning guns is a very good idea if you prefer people to hang rather than shoot themselves. For everything else, it's largely useless.
Other parts of the gun are often serialized, but the serial on the receiver is the one that is considered the serial number of the gun for legal purposes. For collectors, matching numbers on all parts still fetch a premium, especially for antique or just old firearms, such as WW2 rifles.
Speaking of old guns, this is one other interesting side effect of treating the receiver as the gun, and all other components as appendages. Federal law defines a category of firearms called "antique", which is any firearm manufactured on or before 1899. Those are basically completely out of the scope of all existing gun control legislation on both federal and state level (I believe Hawaii is the only exception), unless they fall under NFA (full auto, short barrels etc). You can order them online and have UPS deliver them to their doorstep, no background checks, nothing. If you're a felon, you can still legally own one. And so on.
Now remember that when we say "gun", we really mean "receiver" here. This means that it's perfectly legal to take a receiver from an antique gun, replace the rest with newly manufactured components, and the result will still legally be considered antique. And receiver is the part that normally gets least wear on a firearm (because, on one hand, it's usually metal, and on the other hand, it's not the part that gets most mechanical stress, unlike the bolt assembly and the barrel).
Here is one example of such a thing: an Imperial Russian Mosin-Nagant receiver from 1896, which ended up in the stocks of the Finnish arsenals (quite possibly captured during Winter War or Continuation War, or else it could come from the arsenals they inherited from the Russian Empire when they declared independence), and was then remade into a new Mosin rifle sometime in the 60s, with new barrel, bolt, stock, and possibly the trigger group as well. The resulting rifle shoots just as well as any other modern bolt-action rifle, and ammo is cheap and plentiful.
It's not limited to just bolt-action rifles, either, though those are the most plentiful. But there is a number of antique Mauser C96 handguns around, as well - not quite on par with modern handguns, obviously, what with a fixed 10-round magazine loaded from stripper clips, but still a very capable firearm in its own right. There are plenty of antique revolvers, too.
It's a reasonable request, but only so long as it is framed within a discussion to actually amend the Constitution, and specifically the Second Amendment. The problem is that it's not even on the table - all we have so far are attempts to hack around the wording that is there, by creatively reinterpreting it or selectively ignoring it. It would be a much more straightforward talk if people who don't like guns (all or some of them) would just own up and say that their problem really is with 2A itself, and initiate a constitutional amendment process, just like they did back in the day for the Prohibition.
Getting back to your specific questions, the first thing that is needed is to agree on definitions. For one example, a fully automatic firearm is mostly an unambiguous term, but there are some corner cases such as "bump fire" stocks (which IMO should be considered full auto, but legally aren't, so the definition is not perfect); or a firearm malfunction known as "slam fire" (where the firing pin gets stuck in a forward position rendering the weapon fully automatic to more than a usual extent - it'll fire until there are no rounds in the magazine, even without the trigger being held), which can really happen with any semi-auto firearm and which is never intentional, but which ATF has on occasion treated as full auto.
For another, more interesting example, you mention "assault weapons". As is well known to anyone who looked into this in depth, there's no common definition for these, as it was originally just a hastily concocted and rather arbitrary legal definition for the original Assault Weapon Ban. Today, there's no federal AWB anymore, but there's more than one law project, and then there are various states having their own AWBs which differ in details, so there's no clear single definition. Furthermore, it's not clear how to establish one, because the definitions that do exist don't seem to have any rational basis - it's just an arbitrary picking of mostly cosmetic features.
Flamethrowers are another interesting example. Few people realize that, but not only they are legal to own, it's easier to do so than any firearm, because they are not considered weapons at all (in most states), so there's no background checks and no laws restricting who can own them. And this has some reasoning behind it - turns out that, while most of us are familiar with them in the context of warfare, in practice it's actually a useful tool for farmers to do controlled burns, for example, and occasionally useful for snow removal. Should it be regulated? Probably - it sounds reasonable to me, at least - but we have to consider those other uses when debating this.
The problem though, and the point people are missing (I think, though maybe I'm giving Holder too much credit) is that when they do get a warrant, they still can't access the data. Again, maybe I'm giving them too much credit, but law enforcement should be able to get a warrant and then access that data, through a legal search and seizure.
The problem is that there's no way to do it without having a gaping security hole, because that's what "backdoor" really means. In other words, this cannot be implemented without severely compromising security.
And they have the tools necessary to serve such warrants. Once they have a warrant, they take it to the person who knows the password (which they would have to prove by other means, of course, like having witnesses who saw that person decrypt the data before), and ask them to comply. If they do not, they can be held in contempt of court until such time as they do.
If they have a warrant but you refuse to decrypt it for them, the judge can hold you in contempt until you comply. This has been the case for many years now and does not require any new laws or backdoors.
Water was not diverted directly from the sea. It was diverted from the rivers that feed the sea, and it's still being diverted (the rivers are not going away any time soon), so the benefits remain - what's "short term" about them?
I think the question is, given when it was done and the resources the country had at that time, could it be done right back then on the same or otherwise reasonable timeframe?
Obviously, it can be fixed now, but it sounds like it's way too late for that to have a meaningful effect.
Aral Sea is now split between Kazakhstan and Uzbekistan; Russia is not involved anymore.