When you are purchasing a silencer, SBR, SBS, Machine Gun, AOW, or DD from an out of state resident there are two ways of accomplishing the transfer.
The first and slower way is to do a Form 4 transfer to a local Class 3 SOT dealer. Once this is approved a tax free transfer can be made from that dealer to one in the purchaser's state and then a second Form 4 transfer can be done from the buyer's dealer to the buyer. This will involved 2 transfer fees and generally each dealer will charge a fee for the paperwork and transfer.
The second method involves transferring it directly on a Form 4 to the buyers Class 3 dealer who is located in the same state as the buyer. Once this is approved a second Form 4 transfer can take place from the dealer to the buyer. This will involve 2 transfer fees and fees from the single dealer. This method should be quicker since the dealer to dealer transfer is eliminated.