No you cant walk in with a AK 47 strapped to your leg.
But you can check it with checked baggage.
Has to be in approved container and unloaded.
TSA will check it then you lock it before it is sent to baggage handling.
You keep the key.
If carrying ammo you are allowed up to 11 pounds of this in original packaging or approved TSA one.
Original packing means same as you bought it in the box from the store.
You don't need to declare ammo to TSA in checked baggage.
Not allowed in carry on as common sense applies.
This is the approved way in USA domestic flights.
Why this idiot did this is beyond all thinking.
Check the gun and all OK in checked baggage.
Legal way is easy and no questions asked.