I see no requirement to register an inherited firearm
IIRC the Federal statute makes one exception for receiving a firearm across state lines without an FFL.
By inheritance.
Does not apply to NFA fiorearms however. Form 5 but no tax.
state laws vary, MD requires a 77 for regulated firearms by inheritance
You can pick up the firearm in the state of the decedent without an FFL. If shipped to an FFL, then you do all the paperwork. If you bring the gun back, you do a voluntary registration