> remove a Mauser barrel or index it after reinstalling
There may indeed be issues with the FBI scenario, however, scopes and sights are affixed to the barrel or receiver, not the stock. Reinserting a barrel/receiver/scope assembly into a stock in the field is not complicated. This is not an ideal use of the weapon for precision shooting, but it is not difficult and does not require re-sighting or 'indexing' the weapon.