VFC M&P9 not fully cycling

[SquashyTundra6]

Hi everyone, I have a 7 year old VFC M&P9 that was in storage for about 4.5 years whilst I was out of airsoft. Used it for the first time again yesterday and the slide won’t fully cycle. The pistol was fully disassembled, cleaned out the old grease and then generously lubed up. It is getting stuck every few shots, occasionally it will let off a burst of auto when it should be in semi and then stop again in the half position.
 

If the slide is pulled back quickly by hand it doesn’t stick on the return. Gently pulling it the whole way back will cause it to return half way and stick. When slowly pulling the slide back there is a stop about 1/3 of the way that you have to pull through and then it returns to a normal smooth pull. 

I have seen the glock barrel angle issues and thought that might be the problem, but the barrel moves freely when the slide is jammed. The nozzle itself is slightly sluggish on the return despite being lubed up, it doesn’t however have any issues with sticking to the hop unit etc.? The last thing I can think of is replacing the hammer sear bearing with a rounded one, but I can’t find any for a VFC M&P9, does anyone know if a glock one would fit?  
 

Does anyone have any advice on this? Any help would be appreciated!

 

[johnnyj]

Wow it's been 7 years since these came out.. 

How far did you tare the gun down?

Areas I would be have been looking at are 

Piston cup - lose,damaged, dry

Hammer spring- broken

Broken valve knocker 

But with you describing it jamming is the bottom of hop broken? 

 

[SquashyTundra6]

Wow it's been 7 years since these came out.. 

How far did you tare the gun down?

Areas I would be have been looking at are 

Piston cup - lose,damaged, dry

Hammer spring- broken

Broken valve knocker 

But with you describing it jamming is the bottom of hop broken? 

Thanks for getting back to me! 
 

Pistol was completely disassembled with individual pieces wiped down and lubed where necessary. Piston cup was dry but now fully lubed up, no visible cracking or wear. hammer spring is fine, valve knocker isn’t broken but is worn down in the corners? 
 

Hop unit appears to be in good shape albeit slightly scuffed at the hook, nothing broken off it

 

[SquashyTundra6]

To anyone reading this with similar issues, I found the problem with mine was on the full auto sear coming loose. It didn’t look like anything was wrong until I started specifically inspecting that part. The full auto sear retaining pin was moving out of place when the slide was pulled back causing the slide to stick. On both the side of the pin and and on the edge of the sear as it slightly angled up as the pin moved out. 

 I solved the issue by pushing the pin back in and then slightly mushroomed the end to hold it in place. No more bursts of auto and no more sticky slide problems. 

This is the pin in question, identified at the screwdriver tip. The silver plate to the left is the auto sear, just make sure they are all seated correctly and either glue or mushroom in place. View attachment 86692

Hope this saves someone else a few hours of stress trying to figure out what is wrong!