9mm PCC cycling issues

[MVodopich]

i just built a 9mm PCC.  Pro2a Upper, with Gibbz NRSCU, 16" faxon barrel.  Nordic Components M&P lower, Chip McCormick 3-3.5 lb trigger - after reading several posts, articles, etc, I ended up getting the 7.5 oz KVP buffer, w/KVP Mil-spec tube (came together).

The problem that I am experiencing is that about 25% of the time, the action isn't fully cycling.  Using average, inexpensive 115Gr FMJ.

It ejects and loads another round, but doesn't fully cock the hammer - Could this be caused by a too heavy buffer spring or buffer?  Does anyone have a suggestion for make/model of a more appropriate buffer spring/buffer combination?

[Aircooled6racer]

Hello: Is it not cocking or are you getting hammer follow? Thanks, Eric

[Flatland Shooter]

My first PCC lower built from scratch had a CMC trigger assembly from a .223 in the safe.  Like yours, the trigger failed to reset.  Put it back in the .223 and it runs 100%. 

 

Put a Hiperfire trigger on the lower and it runs just fine. 

[goldfish]

Fire control group issue. 

[phoenixsomd]

I believe the advise in the comments above is on the mark.  If you were having troubles with feeding or ejection then I believe you might look at experimenting with spring-buffer combinations.  A lot of fire control setup for AR's (223/5.56) may not be dimensionally compatible with a AR-9 bolt so, you search till you find the one that other's recommend for your combination of components and give it a try!

[MVodopich]

Thanks for the replies - I've been talking to some other guys too - seems that the McCormick trigger may not be appropriate for this setup.  If anyone has a suggestion for a trigger that has worked well for you in a similar setup, I would appreciate your input.

[L9X25]

The proven triggers are Hiperfire and JP,  they are both reliable with almost every combination. 

 

Anything else is hit or miss, depending on the combination of parts.

 

[Aircooled6racer]

Hello: I have tried 7 different triggers so far and the ones that hold up and work in every PCC AR9mm I have tried them in are the Mil Spec trigger with JP springs and polish job, Hiperfire 24C and 24 3-gun and Eclipse, and also the JP trigger. The problem I have seen is that some of the milspec upper receivers have the bore higher up than some of the others. This causing the trigger not to reset or get hammer follow some times. Thanks, Eric

[MemphisMechanic]

2 hours ago, L9X25 said:

The proven triggers are Hiperfire and JP,  they are both reliable with almost every combination. 

 

And the KE Arms SLT-1 and -2.

 

So far, zero issues in 3 guns locally, two of them running it for the better part of a full season. Designed to fix the problems with other triggers getting beaten to death.

 

Can also put it on SAFE after the hammer is dropped, and pull the trigger over & over in dryfire with the hammer down in dryfire.

[Flatland Shooter]

6 minutes ago, MemphisMechanic said:

Can also put it on SAFE after the hammer is dropped, and pull the trigger over & over in dryfire with the hammer down in dryfire.

 

How did they do that?  I can see where that is a nice feature. 

 

Now I lock back the bolt so I can manipulate the trigger and safety selector.  With the hammer down (bolt forward) I could add magazine reloads to the drill.

[MemphisMechanic]

3 hours ago, Flatland Shooter said:

 

How did they do that?  I can see where that is a nice feature. 

 

Now I lock back the bolt so I can manipulate the trigger and safety selector.  With the hammer down (bolt forward) I could add magazine reloads to the drill.

 

 With conventional trigger assemblies, the hammer is caught by the disconnector on its way back. The heavy bolt in a blowback gun slams hammer into disconnector very hard, and that is what breaks most trigger groups.

 

 There is no disconnector in the KE arms trigger. They figured out a totally different way to do it, and the hammer has nothing to hit on its way back anymore.  It can actually swing back another 30° or so, and would run into the housing for the drop in assembly.

Edited May 25, 2018 by MemphisMechanic