http://www.atf.gov/pub/fire-explo_pub/2005/p53004/27cfr_part478.pdf>
Above is the 'Commerce in Firearms' (GCA68)
TITLE 27 CFR CHAPTER II
In it you'll find this:
Sect 478.11 Definitions...
"Unserviceable firearm. A firearm
which is incapable of discharging a shot
by means of an explosive and is incapable
of being readily restored to a firing condition."
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"incapable of being readily restored..."???
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Also from BATF Ruling #76-25 re: proper method for destroying a damaged firearm by a licensee,,in part reads (last sentence mostly of interest here):
'...Held, a licensee who purchases a
damaged firearm for the purpose of
salvaging parts therefrom shall enter
receipt of the firearm in his firearms
acquisition and disposition record. If
the frame or receiver of the firearm is
damaged to the extent that it cannot
be repaired, or if the licensee does
not desire to repair the frame or receiver,
he may destroy it and show
the disposition of the firearm in his
records as having been destroyed.
Before a firearm may be considered
destroyed, it must be cut, severed or
mangled in such a manner as to render
the firearm completely inoperative
and such that it cannot be restored to
an operative condition....'