The basic “Hubertus Safety Gun” was invented by the forester Franz Feist of Sommerschenburg and protected by the DRPatent No. 7142 in 1879. Feist assigned his patent to Immanuel Meffert, Suhl, who made the guns to Feist’s design. The photo shows the locks of a very early Meffert “Hubertus” gun, still very close to Feist’s original design, in the fully cocked and “fire” mode:

In 1893 Meffert improved the action. He designed the U-shaped mainspring shown above, protected the design change by DRGM Nr. 32200 and used the design at least until WW1.
By 1900 both protections were expired. So F. Jung was free to use the Feist – Meffert lockwork. The 8x72R cartridge was developed by Wilhelm Brenneke, Leipzig, in1898. That Jung drilling most likely dates to 1910 – 14 imho.