As a former UN inspector, I'm also familiar with the level of disarmament achieved concerning Iraq's banned WMD. And during my time in Iraq, 95 percent of the WMD produced by Iraq were verifiably accounted for. But I've always contended that Iraq is a WMD archaeological site, and that if one digs long enough, vestiges of these past WMD programs will be uncovered. Determining whether the discovery of the sarin artillery shell represents such an archaeological discovery, or is part of Saddam Hussein's alleged stockpile of WMD, rests with a full forensic exam of the shell.
The key to whether the sarin artillery round came from an arms cache or was a derelict dud rests in the physical characteristics of the shell. The artillery shells in question were fitted with two aluminum cannisters separated by a rupture disk. The two precursor chemicals for the kind of sarin associated with this shell were stored separately in these containers. The thrust of the shell being fired was designed to cause the liquid in the forward cannister to press back and break the rupture disk, whereupon the rotation of the shell as it headed downrange would mix the two precursors together, creating sarin. Upon impact with the ground - or in the air, if a timed fuse was used - a burster charge would break the shell, releasing the sarin gas.
Many things go wrong when firing an artillery round: the propellent charge can be faulty, resulting in a round that doesn't reach its target; the fuse can malfunction, preventing the burster charge from going off, leaving the round intact; the rupture disk can fail to burst, keeping precursor chemicals from combining. The fuse could break off on impact, leaving the fuse cavity empty. To the untrained eye, the artillery shell, if found in this state, would look weathered, but unfired.