Kel-Tec RDB bullpup 5.56NATO rifle 17" barrel Green

From the manufacturer:

Through an ingenious and simple arrangement we have solved the main disadvantage of Bullpup rifles; case ejection. Traditional side ejection is not ambidextrous and forward eject, like in the FN 2000 or the Kel-Tec RFB, is quite complex.

The RDB (Rifle Downward-eject Bullpup) features a rotary bolt with a spring loaded ejector and an extractor facing down. The spent case is pulled backwards along the top of the magazine and then ejected through a vertical chute. The hammer is U-shaped and runs outside the chute and above the magazine. Obviously, the bolt travel is longer than traditional designs but well within the ergonomic constraints of a rifle. Other advantages are gravity assisted ejection, higher bolt energy at feeding and a slower full auto rate (when applicable).

The RDB is built around a common steel skeleton formed by the receiver and barrel sub-assemblies. Bolt, bolt carrier, firing mechanism, ejector chute and bolt stop are identical for all variations. The short stroke gas operated piston is fully adjustable for different ammunitions and muzzle attachments.