That is correct, Freddyet. Edmund Heckler and Theodor Koch co-founded HK along with Alex Seidel, the designer of the HSc. In 1964, Seidel and Tilo Möller went on to design the Model HK4, an update of the HSc. It was designated the HK4 because it was sold in 4 conversion calibers: .22LR, 6.35mm (.25 caliber), 7.65mm (.32 caliber) and 9mm Kurz (.380 caliber), all in the same box.