Please help with ID

Hi, i was give what looks to me like a South African shotgun shell but has a 303 blank inserted into it. I know i have heard what it is for just cant put my finger on it. Its for firing G5 cannon or something??

Please help!IMG_20181011_0016 IMG_20181011_0017

Simply googling the M8958A1 designation shows that this is a launching cartridge for rifle teargas grenades.


OOPS, I only googled M5A1…

thank you.