The cost of setting up a trust can vary from a small amount for an online form to $100 to $2,500 in lawyers’ fees, depending on location and the type of trust.

The sale and possession of silencers, fully automatic guns manufactured before 1986 and other firearms and accessories that fall under the 1934 National Firearms Act are legal in many states. But the A.T.F. keeps a registry of the firearms and must approve their sale, a process that can take several months, and the buyer must pay a $200 tax.

J. W. Hagan, a computer administrator in Jacksonville, Fla., said he created a trust to buy silencers, which have become popular for target shooting and hunting and can be owned legally in a growing number of states. He said the trust would ensure that if he died, his firearms would remain legal. The trust would also allow his fiancée to use the silencers once the couple married.

“If I didn’t have a trust, she wouldn’t even be able to have the password for my safe,” he said.

David Goldman, an estate lawyer in Jacksonville who, along with another lawyer in Florida, Bob J. Howell, has helped popularize the use of gun trusts six years ago, said most dealers carried out background checks for restricted firearms. He called the notion that criminals might use the trusts to buy the firearms through a dealer “ridiculous.”

“Illegal versions of these items are not only cheaper,” he said, “but you can obtain them six months faster and you don’t have to form a trust, which could be $500 or $1,000 depending on the level, and you don’t have to tell the A.T.F. about it.”

Mr. Goldman, who has prepared several thousand gun trusts and teaches courses on their use, said the trusts have many benefits, like ensuring that firearms were passed on responsibly when an owner dies, keeping them from falling into the wrong hands in a difficult divorce or helping to negotiate moves to other states that might have different gun laws.

“There was never a proper way of dealing with firearms with estate planning and whether beneficiaries were appropriate to receive them,” Mr. Goldman said.