Why does my personally owned weapon have to be added to the commander's hand receipt if I wanted to hold it in the armsroom?

Because if there is ever an installation physical security inspection how are they going to explain an undocumented weapon in the Arms room, everyone from the Armorer up to the CDR is going to jail, that is why.

POWs are authorized to be stored, they have to be accounted for via the installation and the way to do that is to be on the CDR running hand receipt for the arms room, common sense is where the mentality comes from, and it also protects you, because if something happens to it after you turn it in, you are not liable for anything improper that is done with it, doesn't that make sense to you for your protection as well.

This is what I found in AR 190-11:

4–5. privately-owned
weapons and ammunition

a. Commanders will
ensure privately-owned arms and ammunition (including authorized war trophies)
are protected on their installations and
facilities. Based upon local requirements and availability of resources,
Commanders may establish and maintain a system
for the registration of privately owned arms on their installations. Commanders
will—

(1) Secure arms and ammunition in
the installation armory or unit arms rooms in approved locked containers separate from the military
AA&E. Storage requirements in this regulation apply. Installation
commanders may authorize storage of these items
in other locations on military installations, provided they are properly
secured.

(2) Account for and inventory arms
and ammunition.

(a) A DA Form 3749
(Weapons Receipt) will be issued for each privately-owned weapon secured in the
arms rooms.

(b) privately-owned
weapons will be inventoried in conjunction with, and at the frequency of the
inventory of Government weapons.

(c) Commanders will
establish limits on the quantity and type of privately owned ammunition stored
in the arms room, based upon availability of
space and safety considerations.

(3) Post applicable local
regulations and State and local law information on ownership, registration, and
possession of weapons and ammunition on unit
bulletin boards.

(4) Conduct inspections per AR
190–13, paragraph 2–8, and this regulation to ensure proper storage and
control.

(5) Process unauthorized AA&E
per AR 190–22, paragraph 3–4.

(6) Prohibit retention and
storage of incendiary devices and explosives.

(7) Brief all newly assigned
persons on this regulation and subordinate command guidance. All personnel will
be made aware of changes.

b. Personnel
keeping or storing privately owned arms and ammunition (including authorized
war trophies) on

military installation will—

(1) Comply with local regulations
and local and State laws on ownership, possession, registration, off–post
transport, and use.

(2) Store both arms and ammunition
in the unit arms room or other locations authorized by the installation commander.

(3) Follow local security and
safety regulations. Safeguard the unit issued DA Form 3749 for turn–in to the
unit armorer when the weapon is
withdrawn from the arms room.

(4) Withdraw privately-owned
weapons and ammunition from the unit arms rooms only upon approval of the unit commander or the commander’s
authorized representative.

(5) Ship or store arms and
ammunition as personal property, if authorized, per AR 55–355, paragraph 50–12.
When loss occurs, notify the local
provost marshal or security officer immediately.

(6) Comply with the National
Firearms Act of 1968 when receiving or bringing arms into the United States. Automatic arms must be turned
over to the Bureau of Alcohol, Tobacco and Firearms (BATF), or brought under
Army control.