They use another licensee in the buyers state. It's not nearly as magical as Silencer Central makes it out to be and they certainly aren't the first. Silencer Shop did it up until about five years ago for Texas residents. and I know of several dealers who do the same to residents of their states.
ANY dealer can do a "Non Over The Counter Transfer" if state law does not prohibit such:
https://www.atf.gov/file/5221/download
Silencer Central leads you to believe they are shipping direct to your door from South Dakota......they aren't. They use existing FFL/SOT's in each of those states who actually ship the silencer. If a company desires to do business in multiple locations a separate FFL is required for each location.....so Silencer Central isn't doing this from one location in south Dakota.
It sounds wonderful. but unless you are living in a remote area there is little benefit and the process is a slight bit more complicated.
In a "Non Over The Counter Transfer" everything is exactly the same except:
Approved Form 4 (the stamp) arrives at the dealer/SOT
1. You fill out the Form 4473 at home.
2. Attach the sworn statement
3. Attach a copy of the state firearm permit that exempts the buyer from the FBI NICS check. (ATF already has done a NICS check on the buyer prior to approving the Form 4 but does require a copy for non over the counter transactions)
4. The FFL/SOT then forwards a copy of your Form 4473, permit and sworn statement to your CLEO.....and wait at least seven days following receipt by the licensee of either the return receipt evidencing delivery of the copy. THATS SEVEN DAYS
after USPS returns proof of CLEO delivery.
5. Only then can the dealer ship the firearm to your door.
Vs
A normal "Over The Counter Transfer":
Approved form 4 (the stamp) arrives at dealer/SOT
1. You go to dealers premises, complete the Form 4473.
2. Dealer hands you the silencer.