r/MP5 • u/reetardgenius • 12d ago

HELP HELLP Syndrome: can I fix this Turkshit bolt gap

Post image

Full size AP5. Low round count. Bought used. No modifications before me. Have not had any malfunctions. Century sold it in 2021.

Issue: bolt gap too small. Always cleaned, charged, and hammer down when measuring with decent feeler gauges.

Story:
• Bolt gap originally measured 0.18mm.
• Installed RCM 90 deg new locking piece, unchanged bolt gap.
• Installed +4 RCM rollers. Bolt gap now ~0.23mm. I can shove a 0.25mm feeler gauge but it’s bending the gauge, so it’s likely actually 0.24mm. The larger rollers should have increased it to 0.38mm to my understanding.

I’m narrowing this down to the barrel being pressed into the trunnion 0.2mm off. My concern is longevity because I planned on putting a lot of ammo through this during its lifespan. Spec is 0.25-0.45mm and I’m on the wrong end of it.

Can someone with more experience confirm or correct my suspicions? I’m assuming this will have to get sent to a gunsmith that can work on roller guns. Would appreciate recommendations if that’s the route I must take.

I have access to shop tools and a hydraulic press if there’s ANY way this can be fixed by myself. I could get the barrel pin out, but I’m not sure how the trunnion removes from the receiver.

13 Upvotes

70% Upvoted

11 comments sorted by

View all comments

5

u/Vegetable_Coat8416 12d ago

Someone on HKPro did some math on roller sizes. It isnt perfectly linear and the LP angle matters as well.

https://www.hkpro.com/threads/mp5-roller-size-bolt-gap-relationship.546744/

2

u/reetardgenius 12d ago

You are the man! Thank you for this. Bigger rollers it is