Germans had the same type thing on the StG 44. Theirs had a periscope type sighting system. It was invented to be issued to tank crews. The excessive pressure (even with vent holes) caused excessive heat. Barrel life was only in the neighborhood of 250-300 round, so I've been told. It worked, but only for a little while. Most Germans disposed of the device before ever wearing it out.
A similar idea was the periscope aimed sniper rifle from WWI. It had a stock and trigger assembly (sp?) in the shooters hands. ~2 feet above the shooters line of sight was a complete rifle connected by "braces", periscope for aiming, and the trigger linkage. It was used to shoot without having to stick the soldier's head above the trench.
Both were novel ideas to solve a problem and the save lives of the soldiers. Unfortunately neither performed up to standards. But at least both of these inventions allowed for aiming. Unlike the US's design in the linked article.
Wyman
