Hi Polivantage,
I was able to reproduce the crash and have narrowed it down to your .wav files, primarily those used on the shell casing blueprint your pistol spawns. I found that exporting the files and importing them from the desktop in a new project seemed to allow me to play the sounds without a crash, but migrating them to a new project still caused the crash (merely playing the sounds causes the crash to occur, no blueprints are required). Try exporting your sounds and re-importing them to see if this works, if it does not, you will have to work with placeholder assets or alter the sounds to prevent the crash from occurring. I have entered UE-29403 to be assessed by the development staff.