By the end of the WW2 and right after it, Soviets experimented with curved barrel concept. They had some captured Nazi Germany samples of such firearms and tried to make their own versions. One of the host firearms for such a project was a PPSh SMG. This gun had a 30° curved barrel. The test firing showed that the accuracy was unsatisfactory even at close ranges (100 meters). Further development of the curved barreled PPSh was halted.
Curved barreled firearms were developed for many purposes – shooting from the trenches and corners without exposing yourself, shooting from inside the bunkers, protecting the close perimeter of tanks (which main weapons couldn’t reach) etc. Pretty much all of the curved barrel weapon projects in all the countries proved to be unrealistic and not that useful as they seemed to be on the paper.
I think at that point the effort of making a wholly new design outweighed the already tenuous benefits.