<Tr> <Th> Barrel length </Th> <Td> 20 in (508 mm) </Td> </Tr> <Tr> <Th> Cartridge </Th> <Td>. 223 Remington </Td> </Tr> <Tr> <Th> Action </Th> <Td> Gas - operated, rotating bolt (direct impingement) </Td> </Tr> <Tr> <Th> Rate of fire </Th> <Td> full - auto 750 rounds / min cyclic </Td> </Tr>

When was ar 15 first sold to the public