Question for the AR9 PCC guys

[DeauxJoe]

I have an AR9 PCC I put together out of some parts I had lying around. The issue I am having with it is I keep getting double and triple fires with it. I messed with the buffer weight a bit to see if that would help, and it seemed to help some, but not eliminate the issue. Any pointers of where to look? is it as obvious as a trigger issue, or is this in the setup? Parts list below.

Angstadt Arms upper and lower with integral suppressor
TriggerTech AR-9 Adaptable
black rain pcc buffer and heavy spring

 

[roostercogburn98]

is I keep getting double and triple fires with it.

sounds more like a trigger problem to me.

OR your firing pin is moving and striking the primer acting like a fixed firing pin/open bolt setup.

Do you have a good firing pin spring

 

[Old Man with Gun]

Try pulling the trigger with authority and if problem goes away, trigger is the problem or part of the problem.

You may be short stroking, the bolt goes back far enough to eject and strip a round, but not lock the hammer back. When this happens the hammer can fire the next round. Test with one round at a time, if sometimes the next trigger pull does nothing, look at spring and buffer.

You want the bolt to make it all the way back, but not slam into back and bounce back with force. If it is bouncing back hard more buffer weight or spring.

The spring needs to be heavy enough to strip and chamber a round from a locked back bolt. More than that is only helping if buffer is too light.

A suppressed upper has more force on the bolt so a heavier buffer is often helpful.

 

[flogxal]

If you have other buffer springs, try a lighter force/softer spring but keep the heavy buffer weight.

There's a pretty detailed website kept by a guy who spent a bunch of time on blowback AR pattern PCC 9mm build options, trying to optimize recoil impulse, feeding, and avoiding bolt bounce. You might find some thoughts there.

Blowback9.com

No-BS information for the 9mm AR.

blowback9.wordpress.com

 

[Rob01]

sounds more like a trigger problem to me.

I would bet that.

OP I used a standard match AR trigger when I got my PCC and I would get those every once in a while. It was set as heavy as it would go. I pulled it and put in a Timney PCC trigger and no more. That was the only thing I changed. What weight is your trigger set at?

 

[padom]

Yep trigger issue.. not all AR triggers play nice with an AR9.. ive built 4 and I had 3rd burst with Larue MBT2S and a SD3G. Called Larue and they told me their triggers dont work in AR9.

I started only using ALG ACT triggers with their lighter spring and they run 100% over 10s of thousands of rounds. That's what's in both of mine right now.

 

[supercorndogs]

Yep. PCC is kind of picky with triggers. I have an AR stoner enhanced single stage in mine. I am guessing around 5 pounds. It has worked great for super cheap. Lol

 

[Old Man with Gun]

I run the ALG ACT in both of mine with zero issues.
The OP says Trigger Tech AR-9 in build, I assume should work in AR-9, no experience though.

 

[supercorndogs]

"AR9 adaptable."

Has it been adapted?

 

[fedupflyer]

I

Angstadt Arms upper and lower with integral suppressor
TriggerTech AR-9 Adaptable
black rain pcc buffer and heavy spring

What bolt and BCG are you using and is the BCG made for PCC?
What barrel are you using?
What ammo are you using?

The PCC can be finicky, the BCG and buffer should equal (IIRC) 21 oz.

I kinda sounds like you may have a sear engagement issue., as in it is not locking back properly.
I had this issue with a Hyperfire trigger.
Or
You have a firing pin that is out of spec and being slammed to far forward.
Or
The barrel is short throated and the chamber is deep enough for certain ammo. Had this when the PSA PCC first came out years ago and also with a Faxon barrel.

Yes the PCC AR-9 pattern can fire out of battery.
Still have the scars to prove it.

Have you cleaned it well?
PCCz are blow back and dirty by nature and by adding a suppressor its even worse.

 

[anon]

A long time ago, I got a Compass Lake 22lr upper for Service Rifle practice.

It had similar blowback AR issues.

I don't remember the source of the guidance, probably CLE, but the softest hammer spring I could find solved all of the problems.

Cocking the hammer is also part of the recoil energy used.

 

[DeauxJoe]

sounds more like a trigger problem to me.

OR your firing pin is moving and striking the primer acting like a fixed firing pin/open bolt setup.

Do you have a good firing pin spring

I'll have to check, I'm using a Faxton PCC BCG.

 

[DeauxJoe]

Try pulling the trigger with authority and if problem goes away, trigger is the problem or part of the problem.

You may be short stroking, the bolt goes back far enough to eject and strip a round, but not lock the hammer back. When this happens the hammer can fire the next round. Test with one round at a time, if sometimes the next trigger pull does nothing, look at spring and buffer.

You want the bolt to make it all the way back, but not slam into back and bounce back with force. If it is bouncing back hard more buffer weight or spring.

The spring needs to be heavy enough to strip and chamber a round from a locked back bolt. More than that is only helping if buffer is too light.

A suppressed upper has more force on the bolt so a heavier buffer is often helpful.

I like this testing method. I will go this route, thank you.

 

[DeauxJoe]

If you have other buffer springs, try a lighter force/softer spring but keep the heavy buffer weight.

There's a pretty detailed website kept by a guy who spent a bunch of time on blowback AR pattern PCC 9mm build options, trying to optimize recoil impulse, feeding, and avoiding bolt bounce. You might find some thoughts there.

Blowback9.com

No-BS information for the 9mm AR.

blowback9.wordpress.com

Great resource, thank you for sharing

 

[DeauxJoe]

I would bet that.

OP I used a standard match AR trigger when I got my PCC and I would get those every once in a while. It was set as heavy as it would go. I pulled it and put in a Timney PCC trigger and no more. That was the only thing I changed. What weight is your trigger set at?

Currently running at 4lbs

 

[DeauxJoe]

Yep trigger issue.. not all AR triggers play nice with an AR9.. ive built 4 and I had 3rd burst with Larue MBT2S and a SD3G. Called Larue and they told me their triggers dont work in AR9.

I started only using ALG ACT triggers with their lighter spring and they run 100% over 10s of thousands of rounds. That's what's in both of mine right now.

I'll have to check out the ALG trigger. I'm using a TriggerTech PCC trigger, so I would hope it's designed for this.

 

[DeauxJoe]

"AR9 adaptable."

Has it been adapted?

Lol, no adaptation at play.

 

[DeauxJoe]

What bolt and BCG are you using and is the BCG made for PCC?
What barrel are you using?
What ammo are you using?

The PCC can be finicky, the BCG and buffer should equal (IIRC) 21 oz.

I kinda sounds like you may have a sear engagement issue., as in it is not locking back properly.
I had this issue with a Hyperfire trigger.
Or
You have a firing pin that is out of spec and being slammed to far forward.
Or
The barrel is short throated and the chamber is deep enough for certain ammo. Had this when the PSA PCC first came out years ago and also with a Faxon barrel.

Yes the PCC AR-9 pattern can fire out of battery.
Still have the scars to prove it.

Have you cleaned it well?
PCCz are blow back and dirty by nature and by adding a suppressor its even worse.

BCG is a Faxton PCC BCG
Barrel is an Angstadt Arms 16 inch integrally suppressed barrel
Ammo is Win 124gr

 

[Old Man with Gun]

A long time ago, I got a Compass Lake 22lr upper for Service Rifle practice.

It had similar blowback AR issues.

I don't remember the source of the guidance, probably CLE, but the softest hammer spring I could find solved all of the problems.

Cocking the hammer is also part of the recoil energy used.

Good call out, but a 22LR is seriously lacking recoil energy. A suppressed 9mm has more than a 5.56 so kind of opposite problem of a 22LR. I wouldn't mess with hammer spring on a 9mm, asking for ignition problems.

 

[rlsmith1]

Turns out everyone wants 3 round burst guns until it's time to shoot 3 round burst guns

 

[flogxal]

Great resource, thank you for sharing

Yessir. I have a home built PCC AR 9mm and I got lucky that mine ran from the get-go. I did have some odd trigger action at first, using Larue MBT-2 trigger. I am using Timney PCC trigger now and it's fine. I've used it in Steel Challenge and in 2-Gun matches without problem.

I refer to that site I linked when I think about tuning the recoil impulse to make it more game-friendly in Steel Challenge etc. He updates it (or used to) pretty frequently with new parts combos and the results.

The triggers in PCC AR 9mm depend on the bolt carrier contour, if I recall correctly, and not all blowback PCC bolt carriers have the proper contour to reset the trigger fully -- apparently, from what I remember. This is why some triggers that are flawless in regular centerfire AR have issues if used in blowback PCC 9mm settings. TriggerTech's trigger might be fine with some BCGs but not others, for this reason, I think.

 

[DeauxJoe]

Thanks, everyone, it ended up being a combination of too much spring and too little buffer. I corrected those items, and she runs flawlessly now. Thanks for all the help.

 

[TonyTheTiger]

Turns out everyone wants 3 round burst guns until it's time to shoot 3 round burst guns

Facts. I've fired more than my share of accidental bursts, and it's never as fun as you would think. Especially with pistols.