it is only the firearms that are required to be locked away out of sight.
Correct, in the UK rifles.
1/. The firearm must, stored in a lock fast wall mounted [bolted to a wall] gun Safe, the Safe must be an approved safe, approved by the local to you Firearms and explosives section of the local police force.
2/ The bolt for the rifle MUST be stored in a separate lock fast cabinet, again bolted to the wall or? within a separate locked section of the gun Cabinet.
3/. Ammunition MUST be kept in a separate safe, either a wall or floor mounted [secured] safe.
4/. Access to and purchase of Ammunition can only be achieved if the purchaser has a valid Firearms Certificate, every round purchased MUST be recorded on a page of this certificate, once full the page has to be sent to the local to you Firearms and Explosives section of the local Police force, a new clean page will be sent to the License holder.
Now as above this is for the storage and purchase of Ammunition and weapons, but for only one class of available weapons in the UK I have no idea at all what the regulations are in the good old USofA.
Prior to all of the above, the owner of the rifles and holder of a Firearms Certificate has to jump through hoops to get the Certificate.
If even some of the above were to be rolled out in the USA [it would hit the legal interface and prevarication of the NRA, not to mention the Donald's love and inferred "protection" of the NRA ] may especially the Pre-Vetting of persons wanting to hold a license, combined with the banning of certain classes of weapons