[6] Since the mid-80s, the SAF had an outstanding requirement to replace the M16S1, in use since 1973, in part due to licensing limitations that prevented Singapore from exporting the M16S1 or making new assault rifles based on it.

[7] In 1994, a proposal by the SAF was submitted to MINDEF for options to either procure new weapons (thought was given to purchase the M16A2) or to develop an indigenous rifle.

[13] The SAR 21's furniture is made of a rugged, high impact polymer, much of the manufacturing is done utilising CNC machines, with ultrasonic welding for the steel-reinforced receiver halves and the gun barrel being cold hammer forged.

[14] The rifle incorporates various patented safety features, such as a Kevlar cheek plate and a high pressure vent that protects the shooter in the event of a chamber explosion or catastrophic failure.

[3][15] The integral 1.5x optical scope that is built into its carrying handle aids in target acquisition, particularly under low light conditions.

[1] Early users of the weapon in the Singapore Armed Forces experienced many problems due to their unfamiliarity with the bullpup design.

[7] With sluggish operation due to fouling, the gas regulator setting may be adjusted by turning it with a coin, screwdriver, or any other thin flat object.