As far as I know, there is one operational weapon to every reservist (or NSman, if you like). These weapons are vacuum packed (to prevent corrosion) and stored at brigade level facilities all over Singapore. Because they are vacuum packed, it is deemed too costly and time consuming to unpack and repack them for each ICT (given that these occur only once a year). Reservists are instead given training (rather than operational) weapons instead.
When tensions heighten and result in an increase in DEFCON status, reservists will be mobilized outside the annual training cycle and trained for ops. They would then be issued with the operational weapons and ammo. These weapons would then be zeroed and placed in holding camps, in case of open mob. If war does not happen, the weapons would be vacuum packed again.
Also, when the SAF chose to drop the M16 in favour of a newer weapon, one consideration was for a weapon that does not need too much zeroing. That was supposed to have been one of the considerations for the design of the SAR21.
Singapore too cheapskate to give all reservists their assigned weapon that is properly zeroed. When there is a war, many will be Wowo Kings.:(