I'm having issues with my extractor spring and it's driving me crazy, to the point I'm loosing confidence in the gun. I had about 800 rds through the first one and started to get FTE issues and the spring was very loose. Perhaps 100 rds were suppressed.
Replaced it, went through about 400 rds (some suppressed) and it started to wiggle again (replaced it before I experienced any fte issues)
Replaced it again and after 150 rds, it's starting to wiggle once more. This last time, I only shot 115 or 124 factory brass cased ammo and not suppressed.
This last test, I ran only HK mags (all curved) and had zero malfunctions.
Bolt gap is .018 and gun is less than a year old.
Also, running the standard locking piece.
I have an SP5k with over 2000 rds, some suppressed and the spring is still rock solid. Never a single issue.
The MP5 is a clone (will not name as I'm not brand bashing, but it is one of the top three in the nation) and it has the RCM bolt in it. Could the bolt be causing the issue? Would replacing with factory HK possibly fix it?
I understand I can replace the spring with a steel rifle spring but that is not correcting the issue, just covering it up.
Could be lots of issues when dealing with clones. I have a video on my channel covering bolt gap that explains this a bit deeper.
Without having it on my workbench to see for myself, I'd recommend contacting the builder/manufacturer and get them to sort it fo you.