In 1942, after Johann Schmidt retrieved the Tesseract from Norway, HYDRA scientist Arnim Zola experimented on it and subsequently developed this weapon. It was widely used by HYDRA forces. During Captain America's Liberation of Allied Prisoners of War, several of these weapons were captured by the freed American P.O.W.s and used against the prison guards.
To be added
The HYDRA assault rifle fires blue energy pulses that could vaporize humans. It was not as effective against other materials, but could still blast a hole in a brick wall in a barrage of shot. It was also useless against Captain America's Shield, as the pulses bounced off or were absorbed by the Vibranium.