Title I: no paperwork required at the federal level, some states have their own restrictions if the heir happens to live somewhere like CA. The heir can travel to the executor or the executor can travel to the heir, even across state lines, and hand over the gun(s) without violating federal law, again, you need to check state law in the heir's state to make sure such a transfer comforms with state law.
Title II: the firearm will transfer tax-free on a Form 5 from decedent's estate to heir, check state laws to make sure the firearm is legal in the heir's state first.