Telescoped cartridges reduce ammunition weight by 50%, though firearms require special modifications to fire it.
Telescoped cartridges are an evolution of polymer-cased ammunition, in which the bullet is contained within the shot itself, rather than protruding out. This allows ammunition to become far more compact and lightweight. However, telescoped rounds share the same inherent problems as polymer-cased cartridges, and if not manufactured correctly may also suffer from poor reliability.