Fill out the proper paperwork, pay $200 (per device), wait for the feds to get done crawling through your bowels with a magnifying glass, pick up your fully automatic firearm, short barreled rifle or short barreled shot gun. Just make sure you keep that paperwork with the item at all times. People with full autos and SBRs are the most highly vetted individuals on the planet. Way more vetted than the current usurper in chief.
There are two legal ways to avoid the fingerprinting, mug shot, background check, and sign-off by the chief LEO of your county to complete your ATF Form 4.
You can form an LLC corporation to hold your Class III items as "corporate assets". You as CEO and whomever else you designate as a "corporate officer" may use "corporate assets".
You can form a revocable trust to hold your Class III items as "trust assets". You as trustee and whomever else you designate as a trustee may use "trust assets".
These are possible because in the eyes of the law corporations and trusts are "legal entities". They are treated as a living person, they have rights, in the case of the corporation they pay taxes, but are incorporeal. That is they are not flesh and blood hence they have no fingers to print, no mug to photograph, and they get a pass on the background check and sign off by the LEO. By the way, the sign off is required if you file the Form 4 yourself but is discretionary on the part of your Sheriff. If he says no you are done right there.
The major differences between the two being corporations must be registered in the state in which they are incorporated. They must file an annual report with the state, and may be required to pay taxes if they turn a profit. The IRS may at some time enter the picture if you haven't filed a corporate return. They may declare your corporation is not a business but a hobby and yank your corporate standing.
Trusts, on the other hand, are only required to register in twelve states (and that is a "may" requirement, not a "must"). There is no requirement for annual reporting and no taxes. Thus, trusts function well below the "radar" and present a very discreet face to the world.
In either case you are going to need professional help in setting up the legal entity. To assure your success you should seek out a lawyer who handles "gun law" cases in your state of residence. There are law firms (Legal Zoom dot com) that do corporate and trust filings but have no experience with the gun laws of your state, AVOID going cheep and get the job done right the first time. There are web sites that can guide you to qualified law firms that will work with you to make sure you don't foul up. Plan on spending at least $1000 to get an iron clad package.
The completed Form 4, your certified check for $200, and a copy of your corporate or trust documents gets forwarded to the Class III FFL dealer from whom you are purchasing your "asset". He then completes the form by filling out a description of the purchased item with serial number, the address of his place of business, and the signature of the Class III licensee. He then forwards the entire package to a BATF examiner. What happens next is going to take time (6 months??) but in the end you will get what you want, guaranteed. If you file personally, no guarantee.
Regards,
GtG
PS No matter how you acquire a Class III item, file personally, shell corporation, or trust there are many ATF rules governing transportation of, use of, storage of, and ultimately disposition of your new toy. As well as the necessity of keeping ATF current on your home address. Your lawyer can fill you in.