The Reising gun was adopted by the Marines early in WWII, and was used on Guadalcanal.
In Marine combat use it was a miserable failure.
Problems were a poor blue finish that rusted in minutes in the humid tropics, a wire folding stock that would collapse in use, and a low magazine capacity. Choices were a 20 round magazine, or a ridiculous 12 round magazine.
The biggest problem was that the weapon jammed badly. This was caused by dirt and fouling collecting in the locking recess in the receiver. Because of it's location, it was difficult to keep the area clean, and the gun developed a reputation as a "Widow-maker", for the excessive failures.
Many disgusted Marines threw the guns away and stole Army weapons to replace them.
Shortly thereafter, the Marines discarded the Reising to the regret of no one.
Strangely, after the war, many Reisings were given or purchased by police departments, where they were used successfully for many years.
Most of the available Reising's are these ex-police guns.
In civilian use, a well cared-for gun with the wooden stock and the larger magazine was an effective weapon, but it never could shake it's war-time reputation.