Start by closing the engine and download the file below for your projects engine version, then open your project files in windows explorer and go to the Content/SurvivalGameKitV2/Effects folder and replace the P_MuzzleFlash file with the P_MuzzleFlash file in the folder you just downloaded.

Unreal Engine 5.0 – 5.2

https://www.dropbox.com/scl/fo/9a9uj3afxqk7dsrkz6xjg/AHoiPD1aHVPJAp3PPYGIxds?rlkey=vu2ali3ctr6u9o7x3n6460qgl&dl=0

Unreal Engine 5.3 – 5.5

https://www.dropbox.com/scl/fo/w0tkehj1cdpmgapwesix5/AJe0MocEFTPBhDsKypKBVok?rlkey=h241zn66iq8p0kwef5gaglzvd&dl=0

Then open your project and go to the BP_MasterRangeWeapon then open the Shooting collapsed node and copy the video below.

Note – If your using a custom niagara effect for the weapons muzzle flash, you will need to go to the niagara effect and in its main system state make sure its Loop Behaviour is set to Once, its Inactive Response is set to Kill and then use the Loop Duration to control the length of the effect.