VALMET 82

The Valmet 82 is a bullpup 5.56x45mm.   This rifle had a lightened bolt carrier and thinned barrel to reduce weight.

This rifle would have certainly been adopted by ever major military in the world if not for the lack of a bayonet lug.  Furthermore, no other military was ever able to duplicate the revolutionary sighting technology used on this weapon...and you thought the sights just got bent.