PCC 9mm Going Full Auto - Why?

[cbrussell]

My friend has a new PCC 9mm rifle with the following specifications.

• Spikes Tactical lower
• Unkown manufacture 16 inch barrel/bolt/ upper
• Arma Spec.  one piece captured buffer  rated at equivalent weight of 5.4oz. (Note - the installation of this part required the removal of the bolt weight)
• Timmy PCC trigger left as is from the factory - approximately 3.2 lbs pull weight
• ETS and Glock magazines - both had same issue
• Anti walk pins
• 124 grain Top Gun ammunition rated at 1050 FPS  out of a 5 inch barrel

The gun seemed to work for a few rounds, then the trigger seemed not reset, with some manually ejected unfired rounds having a very slight firing pin strike mark, hardly enough to see. Then the gun began going full auto. 

 

Any ideas on where to start to solve this issue?

Thanks for the help.

 

[TeedOff]

First thing I’d check is the trigger. Specifically the disconnector and disconnector spring.

[cbrussell]

This is a Timmy drop in trigger assembly, so I think no way to check those springs?

[TeedOff]

Can you try a different trigger then?

[bigfish]

Verify the firing pin is loose in the bolt and not hanging up and that the FP spring is good as to not cause a slam fire, after that your kind of down to a trigger issue

Edited March 22, 2020 by bigfish

[MoRivera]

9 hours ago, TeedOff said:

First thing I’d check is the trigger. Specifically the disconnector and disconnector spring.

+1.  This happened with a Rise Armament unit in one of mine.

[philmadxx]

12 hours ago, cbrussell said:

• Spikes Tactical lower
• Timmy PCC trigger left as is from the factory - approximately 3.2 lbs pull weight

I had the same problem - with the same parts above.  Trigger was the issue not sure why.  Tried 4 other triggers, all worked 100%, Timney did not - randomly would go full auto.  I put it into an AR - no issues there. 

Good luck

Phil 

[egd5]

I had the same issue with a Timney in my previous pcc. I called them and they told me I had the wrong trigger for a pcc. I don't remember what was the wrong one, it was the difference between a single stage and a two stage trigger. But call them and they can sort it out for you. They exchanged mine at no cost I believe, but it's been a few years.

[philmadxx]

On 3/22/2020 at 10:24 AM, egd5 said:

I had the same issue with a Timney in my previous pcc. I called them and they told me I had the wrong trigger for a pcc. I don't remember what was the wrong one, it was the difference between a single stage and a two stage trigger. But call them and they can sort it out for you. They exchanged mine at no cost I believe, but it's been a few years.

 

Agreed - since I bought my Timney, they've come out with a specific PCC trigger - based on their other products, I would guess it is first rate and would not have the full auto issues - although I haven't tried it.  I don't think you get a really low pull weight with it - maybe 3.5 lbs. 

Phil 

[TRUBL]

Over here at TACCOm, we procure our competitors parts for comparison from time to time......the other day we got in a Arma SPec 9mm recoil system. On the looks alone, very nice and a decent design. AND....the price is right for sure. We've not tried it in a PCC as of yet, but the one thing we noticed right off is that we feel the that the main recoil spring seems too light. I'm pretty confident that it will work fine for factory 147s, but I would like to see a heavier spring for 124s and 115s (personally). Buffer weight, mmmmmmight be a little on the light side but at almost 20 ounces total for the bolt/buffer combined that should be ok. Of course, being the salesman and owner of TACCOM, I'm gonna tell you that our set is waaaaaay better......but int he end, you get to decide whats best for your set up and I'm totally ok with that. I'm just trying to give information so you can make a wise choice. I think that with near min PF loads it may be an economical set up. In your set up.....you may be sending eveything back way too fast and not giving enough dwell time on the dissconnect.

 

Not a real fan of Timney triggers, have always found that I get a hard trigger slap on the reset in PCC weapons.......if you are experiencing that, I can see why you'd get doubles.....looking at a different set up for the trigger may be in order.

 

On the bolt.......that seems to be the wild card here. If it's aJP or TACCOM, those bolts will pretty much work with any decent trigger out there. The geomtry of depth of the ramp is very similar to the std 556 bolt carriers. Again.....speed of bolt can be an issue.

 

As to addressing your problem, all speculative as I am not there. I'd check for some issues like trigger slap and overall feel of the firearm in recoil.....if seems hard or fast.....you have a buffer issue to address. You may also want to look at the trigger or possibly the the bolt. Only suggestions.....again, if I was there, it would be an easy diagnosis. Not being there......I can only give pointers on what to look for. Ammo as described should not be an issue if it's doing what is advertised......but you can always try another ammo too.

[egd5]

In other words--the voodoo science of pcc tuning.

[cbrussell]

Thanks to all who posted their suggestions. As a follow up, my friend changed the Arma Spec. buffer system out with the standard spring buffer which came with the gun. Worked great with no full auto or burst problems. He then tried a Taccom bolt assembly; tha too worked, however, he sheared off the bolt stop. So he is now searching for a stronger bolt stop. I think he is also going to purchase the Taccom buffer system as well. 

[TRUBL]

38 minutes ago, cbrussell said:

Thanks to all who posted their suggestions. As a follow up, my friend changed the Arma Spec. buffer system out with the standard spring buffer which came with the gun. Worked great with no full auto or burst problems. He then tried a Taccom bolt assembly; tha too worked, however, he sheared off the bolt stop. So he is now searching for a stronger bolt stop. I think he is also going to purchase the Taccom buffer system as well. 

good choice!!

Follow up to the ARMA Spec recoil system 9mm, the one I received......you can not tell the difference between the first and second stage......I mean ZERO!! Again.....nice concept, crappy application. I truely believe that the 2nd stage needs a spring that is about 5 to 8 pounds stronger than what is supplied with the system. Anyone one else have that system?.....try this, pull it out of your weapon.....close your eyes, push down on the system to collapse it......I'll bet you can't feel the second stage. BUT.....if you do, I'd like to know.