I thought I'd summarize the snake pit it is to wade through.
State laws vary. My state has no restrictions on weapons at all. Non-firearms are not weapons. Firearms are unrestricted. By federal law, you have to be 21 to buy a handgun from a dealer, but face-to-face sale or transfer (Such as to my daughter when she turned 18) are not restricted. I can, and have, walked into a show, plopped down cash, and walked out with a dozen revolvers for my collection. From a dealer, or from out of state, I can get most collectibles on my collector's license by swapping numbers. If I buy a regular firearm from a dealer, they have to call through the FBI and I fill out a page. It usually clears within seconds.
National Firearm Act restricted weapons include:
Full auto. In 1986, the manufacture of new, transferable machine guns terminated. The ones in existence and on paper are all there are. Once an item is a machine gun, it is ALWAYS a machine gun, it cannot legally be made into a non-machine gun. It can only be transferred or destroyed. Dealer samples (For gov't or overseas sale) still exist. Those made before the deadline can be owned by a retired dealer, but can only be sold to another dealer. Those made after the deadline can only be owned as long as the dealer has his license with the Special Occupational Tax for Class III (NFA Weapons).
Short barreled rifles (under 16") and shotguns (under 18"). These can still be made by a mfr or individual.
Destructive Devices. Over .50 cal and not in a sporting caliber (you can get a sporting caliber approved fairly easily, as long as it's not designed for a self-loading weapon), explosive shells, grenades and launchers, non-black powder cannon, Striker shotguns (by name, added in 1993). These can still be made.
"Silencers." (Yes, they are considered a "firearm.") These can still be made.
Any Other Weapon--pistol shotguns, guns concealed in phones or such, anything that isn't held like a typical gun when in use. These can still be made.
To manufacture any of them requires approval on a Form 1, and a $200 stamp (literally, a stamp as for a letter shows up on a piece of paper). AOWs are only a $5 stamp, if made by a mfr, $200 if made by a non-mfr. Transfer is only $5. The processing time on Form 1 is several months.
From mfr to dealer or owner to dealer takes a Form 3, which approves in about a week. There is no fee.
From mfr or dealer or individual or corporation to another individual or corporation takes a Form 4 transfer, $200, and several months.
The paperwork must be in order before the transfer can take place.
Upon death, the weapon can be transferred to relatives on a Form 5. Form 5 is also used to reactivate a de-activated weapon (usually a war trophy).
Note I said "Corporations." When the Act was set up, banks, railroads, security companies, etc, still wanted access to machine guns and SBRs. So a corporation can own them. The corporation can designate which officers may possess the weapons.
An individual who possesses such must be immediately present in sight of anyone using his Class III weapon.
Therefore, as with others, my wife and I have an incorporated trust that owns the weapons, and as the children reach age 21, they will be added as officers of the trust. The language states that if any member becomes ineligible (such as medically or legally) they are removed from the trust. We can also designate temporary members during events, so we don't have to take the weapon to the bathroom, for example. The trust has its own bank account and official correspondence, and an attorney on retainer.
Previously, individuals needed approval from the local chief law enforcement officer. Corporations did not. Individuals had background checks. Established corporations only needed a single check.
Some idiot in California added a felon friend to his silencer trust and got caught. Ergo, the obvious bureaucratic solution was to punish all the law abiding.
Now, every trust member must submit paperwork, and law enforcement is notified but may not reject. However, new members added to the trust later are only checked going forward on purchases, not at time of joining. So this law completely fails to address the issue that allegedly caused it.
So, for the two machine guns and suppressor we just purchased, and the SBR I intend to convert from a pistol, my wife and I must submit, FOR EACH:
Two sets of fingerprints (I am an immigrant and former military. My prints are on file with ATF (Bureau of Alcohol, Tobacco, Firearms and Explosives), FBI (Federal Bureau of Investigation), ICE (Immigration and Customs Enforcement), DoD (Dept of Defense), DIS (Defense Investigative Service), USAF, US Army). She holds a security clearance and conducts forensic investigations for a major international defense contractor. Her prints are on file with at least FBI, DoD and DIS.
Two passport photos.
The Form 4 in duplicate for three of them and the Form 1 in duplicate for the SBR.
A valid reason to own each weapon. I have seen an approved form that said the purpose was "To kill zombies." That's not an illegal purpose, so it's good enough. We're listing "investment and research."
$200 for each stamp.
Meanwhile, our dealer who has a range so we can shoot, must accompany us while we shoot our property, and must keep them in his vault until sometime late in 2018-early 2019 before we can take them home. The pistol I'm converting stays here, but can't be converted until the form returns.
The suppressor only cost $500.
Because the "new" submachine gun we're purchasing was made in 1986(!) and there are a very finite number, that costs...
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$13,000.
And the WWII vintage Reising Model 50 I found is a bargain at only...
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$4700.
Plus fees, paperwork and wait time. And the dealer is only charging $50 each to transfer them to us (Most places charge $100).
It's a free country, and I have all the licenses and permits to prove it.