I have one of these works really well , got it from HK and didn’t pay anything like this mich ! https://www.weapon762.com/magazine-drum/872-iron-airsoft-1000rds-sound-control-m4-mag-drum.html?search_query=Drum+mag&results=10
https://www.weapon762.com/magazine-drum/872-iron-airsoft-1000rds-sound-control-m4-mag-drum.html?search_query=Drum+mag&results=10