Burst fire with Ruger PCC & VQ trigger

[jrdoran]

Need some help on how to debug and resolve;  I'm not a trigger expert, but do understand the other aspects of the Ruger PCC pretty well.

 

Last night I had 2 separate instances of burst fire in my 9mm Ruger PCC with Volquartzen TG9 trigger.   One for 2 rounds, one for 5 rounds.   In several thousand rounds I have never had this issue prior ( I did switch ammo last night ) 

 

Some background.   I normally shoot very light 80pf loads, but last night was using some 109pf loads ( still light by standards ) ;  The TG9 trigger came directly from volquartzen but took 3 round trips for them to get it to a 2lb trigger pull.  Out of the box it was closer to 3.25lbs.   

 

 

I will call VQ and I suspect their tweaks may have contributed.   

 

Others who have modded their own triggers have reported burst fire instances.    Interested in points of view, ideas.    For now I may put the stock trigger back in which is frustrating as I need a few good match results for some steel challenge qualifiers.  

[SnipTheDog]

You could call it a feature and sell your PCC as a sub-machine gun for big dollas.

[racerba]

4 hours ago, SnipTheDog said:

You could call it a feature and sell your PCC as a sub-machine gun for big dollas.

and get arrested in the mean time...

[SteelCityShooter]

I would call VQ IMMEDIATELY! They have to know about this problem and have to modify your trigger to prevent it.  It is quite possible a 2 pound trigger pull can't be had safely with this gun.

[Siberian]

I think PC9 needs quite a bit of sear-hammer engagement due to it’s heavy bolt cycling above the trigger. It seems when the bolt closes, it might induce just enough shock and rotation for the sear to skip. I tried the 10/22 Kidd trigger job kit, the trigger felt perfect and passed function checks, but also caused bursts with live ammo. A 6.5” PC Charger with a comp and tele stock remained very controllable, compared to AK-74U in 5.45x39, albeit the rate of fire was a bit high. Finished the session with 1 round per mag (was chronoing a bunch of new loads), and returned things back to stock asap.

Your PCC has a super light front end, right?

[jrdoran]

1 hour ago, Siberian said:

I think PC9 needs quite a bit of sear-hammer engagement due to it’s heavy bolt cycling above the trigger. It seems when the bolt closes, it might induce just enough shock and rotation for the sear to skip. I tried the 10/22 Kidd trigger job kit, the trigger felt perfect and passed function checks, but also caused bursts with live ammo. A 6.5” PC Charger with a comp and tele stock remained very controllable, compared to AK-74U in 5.45x39, albeit the rate of fire was a bit high. Finished the session with 1 round per mag (was chronoing a bunch of new loads), and returned things back to stock asap.

Your PCC has a super light front end, right?

 

I think you are spot on.   This goes to the other points about can this trigger design support a light engagement on the PCC platform.  Clearly on 10/22 rimfire it is possible to get <2lb.      Yes, my PCC has a 5" barrel that is shrouded out to 16" and is very light.  

 

  

[ysrracer]

On 10/28/2020 at 6:16 AM, jrdoran said:

Some background.   I normally shoot very light 80pf

 

Is an 80 power factor enough to cycle the gun?

[jrdoran]

I regularly run 61pf.    I have not been able to recreate the burst fire issue.  I cleaned the trigger with 'brake cleaner' and then compressed air.   I also added a bit more over travel to the trigger.   Functioned tested with 100 rounds.   Shot an 8 stage steel match w/o any burst fire.   

[IronicTwitch]

61PF?

 

22lr (40gr x 1200fps) is 48PF

 

I'd echo what Siberian said above.

Edited November 16, 2020 by IronicTwitch

[ysrracer]

2 hours ago, jrdoran said:

I regularly run 61pf

 

Am I allowed to impugn one's manhood? Or will I get banned?

 

(Asking for a friend)

[jrdoran]

2 hours ago, ysrracer said:

 

Am I allowed to impugn one's manhood? Or will I get banned?

 

(Asking for a friend)

 

The line forms to the left...        

[jrdoran]

2 hours ago, IronicTwitch said:

61PF?

 

22lr (40gr x 1200fps) is 48PF

 

I'd echo what Siberian said above.

 

Correct and we do use mini mags as the comparison so you are spot on.  

[egd5]

Can I ask what bullet, powder and load info you are using to get 61 pf? Or even 80 for that matter.

[ysrracer]

Just now, egd5 said:

Can I ask what bullet, powder and load info you are using to get 61 pf? Or even 80 for that matter.

 

I've had squibs that had a higher power factor

[jrdoran]

16 minutes ago, egd5 said:

Can I ask what bullet, powder and load info you are using to get 61 pf? Or even 80 for that matter.

@tomvloads for me, but here is what I believe to be the formula.  I have 100% cycle reliability.   

 

- 95gr Montana gold bullet;  Personally I prefer the 100gr Berry bullet given it is less stubby and just seems to run better.

- 2.4 gr N310 powder;  2.2 when using 100gr Berry.

- 1.08 OAL, but currently experimenting with 1.05

 

Velocity ~ 650-700 FPS

I forget the Std Dev. 

[egd5]

Thanks.

[jrdoran]

This is also a popular load for shrouded barrel PCC 

2.5gr of W231 under 124gr Berry's RN.  OAL 1.135;   Chrono's about 630fps

 

 

Edited November 17, 2020 by jrdoran

[ysrracer]

5 hours ago, jrdoran said:

This is also a popular load for shrouded barrel PCC 

2.5gr of W231 under 124gr Berry's RN.  OAL 1.135;   Chrono's about 630fps

 

 

 

Same as my squibs

[lwink]

I have had this happen twice on different platforms, both with relatively high cyclic weight (heavy buffers, bolts, and strong springs), and discovered two things:

 

1. Shooting off a bench, the gun actually more or less bump fired. Moved back toward me on recoil, and without offhand support the cyclic mass moved the gun, and trigger, forward into my finger and fired again. Never happened in thousands of rounds but put in a heavier buffer and beefy spring to play with things and sure enough, wouldn't have believed it until I heard about the possibility and really paid attention. There are ways to mitigate with more trigger control, but having been a bolt guy my whole life until a few years ago never really needed to learn about this possibility.

2. Had one setup that I dropped an adjustable trigger in and really had it too light/too little engagement.  I don't know for sure, but the rig never had an issue previously, new trigger and I got some random doubles, back to a different trigger and never saw it again.  I can only think that there was so little engagement it could jar itself into doubles or beyond, which means it probably wasn't drop safe, at least not with the safety off, and not really what I needed.

 

Maybe one of those scenarios can give you some things to think about or rule out?

[Siberian]

In my case, it was probably a combination of 1 and 2. I tried to induce a drop fire, but the trigger functioned as intended, until the time came for a live fire test.
 

@jrdoran: did you have to do any mods to the bolt / recoil assy to run such light loads? My Charger had a couple of feeding stoppages with 127 PF reloads during a recent match. It felt like the bolt did not cycle completely: empty case ejected, new round stripped from the mag, but the bolt did not fully close. I rack the charging handle, end up with two rounds in the feeding path. Day two, switched to cheap factory 115 gr FMJ Remington, no issues.
 

The reloads were 115 gr plated hollow points, N320, if that matters. The same bullets were 100% reliable at 131 PF, with CFE Pistol powder.

[jrdoran]

Internals are stock except Mcarbo extractor and recoil pad.  I did smooth out any rough areas of the receiver with 1000 sandpaper.    I keep it very clean and liberally use mobil 1 oil to keep things slick.   It does get quite dirty.      

 

I have let others with bone stock ruger pcc try my ammo at matches and it runs w/o issue.  The stock extractor is crap.   

 

@lwinkAt this point, I am chalking it up to not enough reset, possibly debris,  and  poor trigger control on the night where I experienced bursts.

[jrdoran]

SOLVED:   

 

I borrowed a friends stock Ruger pcc rifle for testing and installed my problematic TG9 trigger assembly and had zero burst fires.    After  some soul searching I started swapping parts, weighing parts, and measuring parts. 

 

I use an mcarbo shock buffer at the rear of the recoil spring.  https://www.mcarbo.com/ruger-pc-carbine-shock-buffer.aspx    it is a small amount thicker ( .120 ) than the stock buffer.   This is apparently enough to keep the bolt from fully cycling and reseting the hammer in the TG9 trigger assembly, especially with stronger ammo pf100+ and is most frequent at pf135.   

 

Swapped mine to stock and I get to enjoy the capabilities of the VQ trigger without the drama of burst fire.  

 

[shoresroad]

@jrdoran

 

Sorry to necro this post, but there is very little information on the topic of trigger mods for the Ruger PC Carbine, and most of them are at least a couple of years old.  Thanks for your "Solved" post above.  I have been having problems with burst fire and/or my trigger not resetting after installing the MCarbo shock buffer and the Volquartsen Target Hammer (which has been discontinued by Volquartsen but is still available "new" on eBay from a Volquartsen dealer).

 

The Volquartsen Target Hammer kit reduced the trigger pull on my new Ruger Magpul PC Carbine from 5.5 lbs to 3.5 lbs, which is where I want it.  And on the first 200 rounds of PF130 I had no problems.  But this is going to be a home defense rifle, and when I moved up to Winchester Ranger 127 grain +P+ RA9TA to sight in my red dot, here came the burst fire/trigger reset problems.  So same problem, but at a higher PF threshold.

 

So, after reading your post, I'm going to start by removing the MCarbo shock buffer.  I also have a Tandemkross Shock Block that I'm going to measure.  If it is thicker than the stock shock buffer, then I'll stick with the stock shock buffer and see how things go.

 

Thanks for your information.  I'm sure that others will continue to find it helpful in the future. 

Edited August 4, 2023 by shoresroad

[jrdoran]

Will be interested to hear how the two shock buffers compare.  That you for measuring and it will add to the discussion and data we have.  

 

Post back and let us know how your experiment goes.

[Zachjet]

My stock PC nine did this at a match once. I took it home and scrubbed it really good and haven’t had a problem since. Shot two matches since then.