<Table> <Tr> <Th colspan="2"> SAR 21 </Th> </Tr> <Tr> <Td colspan="2"> The SAR 21 with the attached Round Corner Firing ( RCF ) module </Td> </Tr> <Tr> <Th> Type </Th> <Td> Bullpup assault rifle </Td> </Tr> <Tr> <Th> Place of origin </Th> <Td> Singapore </Td> </Tr> <Tr> <Th colspan="2"> Service history </Th> </Tr> <Tr> <Th> In service </Th> <Td> 1999 -- present </Td> </Tr> <Tr> <Th> Used by </Th> <Td> See Users </Td> </Tr> <Tr> <Th colspan="2"> Production history </Th> </Tr> <Tr> <Th> Designer </Th> <Td> Tuck Wah Chee and Felix Tsai of Chartered Industries of Singapore ( CIS , now ST Kinetics ) </Td> </Tr> <Tr> <Th> Designed </Th> <Td> </Td> </Tr> <Tr> <Th> Manufacturer </Th> <Td> CIS : 1999 -- 2000 ST Kinetics : 2000 -- present </Td> </Tr> <Tr> <Th> Produced </Th> <Td> 1999 -- present </Td> </Tr> <Tr> <Th> Variants </Th> <Td> See variants </Td> </Tr> <Tr> <Th colspan="2"> Specifications </Th> </Tr> <Tr> <Th> Weight </Th> <Td> SAR 21 : 4 kg ( 8.82 lb ) SAR 21 GL / M203 : 5.3 kg ( 12 lb ) SAR 21 P - Rail : 3.6 kg ( 7.9 lb ) SAR 21 MMS : 3.5 kg ( 7.7 lb ) SAR 21 Light Weight Carbine 3 kg ( 6.6 lb ) </Td> </Tr> <Tr> <Th> Length </Th> <Td> 805 mm ( 31.7 in ) ( SAR 21 , SAR 21 40 GL / M203 , SAR 21 P - Rail ) 680 mm ( 26.8 in ) ( SAR 21 MMS ) 640 mm ( 25.2 in ) ( SAR 21 Light Weight Carbine ) </Td> </Tr> <Tr> <Th> Barrel length </Th> <Td> 508 mm ( 20.0 in ) </Td> </Tr> <Tr> <Td colspan="2"> </Td> </Tr> <Tr> <Th> Cartridge </Th> <Td> 5.56 × 45mm NATO </Td> </Tr> <Tr> <Th> Caliber </Th> <Td> 5.56 mm ( 0.22 in ) </Td> </Tr> <Tr> <Th> Barrels </Th> <Td> Single barrel 1 : 12 '' and 1 : 7 '' twist options </Td> </Tr> <Tr> <Th> Action </Th> <Td> Gas - operated , rotating bolt </Td> </Tr> <Tr> <Th> Rate of fire </Th> <Td> 450 -- 650 rounds / min </Td> </Tr> <Tr> <Th> Muzzle velocity </Th> <Td> 970 m / s ( 3,182 ft / s ) ( M193 ) 945 m / s ( 3,100.4 ft / s ) ( SS109 ) </Td> </Tr> <Tr> <Th> Effective firing range </Th> <Td> 460 m ( M193 ) 800 m ( SS109 ) </Td> </Tr> <Tr> <Th> Feed system </Th> <Td> 30 - round detachable box magazine ; proprietary or STANAG magazines </Td> </Tr> <Tr> <Th> Sights </Th> <Td> 1.5 x or 3x optical sight ; back - up iron sights </Td> </Tr> </Table>
what is the back up sight used in sar 21 in the event of optical scope failure
iron sights