if you are hands on person and taken the bolt apart before I would suggest trying this
https://www.ebay.co.uk/itm/Airsoft-CNC-Machined-Power-Down-Valve-Set-For-KSC-KWA-S7-NS2-MP9-MP7/141409941879?epid=935665992&hash=item20ecb07977:g:rCAAAOSwGvhUGNbn
iv run them in mine and I CQB safe at...