Given that it is Monday morning I will am going to avoid making this post too text intensive and just pass on some interesting images today. These are not really that useful for self-defence but they may interest or amuse, which is not a bad thing for a Monday morning.
What you are seeing is an attachment for an MG-42 that allows it to be aimed and fired from a trench or foxhole without the user exposing their heads. Similar devices date back to the First World War. Trench warfare was a predominant facet of this conflict and understandably a number of devices to facilitate firing from trenches were developed. Many of these devices adapted the standard service rifle, which often necessitated some mechanism to work the bolt action the chamber a new round. There were also periscope equipped Lewis Guns.