The gun is property of the estate. OP is a bailee. If an executor or administrator is appointed, it should be given to that person upon presentation of the court appointment document, with a receipt received. Some states may have an alternative method of administration of small estates involving affidavits. The gun should remain in safekeeping until given to a person authorized by law to administer it.
According to the initial post, the owner was afraid that his son would steal the firearms. This does not indicate an intention to give them to him. Doing so would contravene the owner's instructions and could result in an additional felony conviction for the son as well as the person who gave it to him. OP has no ownership interest or authority to sell, purchase or dispose of the firearm. The probated will of the owner, or the laws of intestate succession, should ultimately control ownership.
Do not rely on internet legal advice. Do not rely on other people's lawyer's advice.
According to the initial post, the owner was afraid that his son would steal the firearms. This does not indicate an intention to give them to him. Doing so would contravene the owner's instructions and could result in an additional felony conviction for the son as well as the person who gave it to him. OP has no ownership interest or authority to sell, purchase or dispose of the firearm. The probated will of the owner, or the laws of intestate succession, should ultimately control ownership.
Do not rely on internet legal advice. Do not rely on other people's lawyer's advice.