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Help me tune this PCC: FM upper, JP SCS, Hiperfire.

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I have a 16 inch Foxtrot Mike glock upper/BCG with JP SCS (3 tungsten and 2 steel weights) and Hiperfire competition trigger with lightest (no color) springs. The lower is a New Frontier Armory C9 (Glock pattern) with a carbine buffer tube. Anti walk pins, I think JP.  Ammo is factory Blazer 124gr.


This combo goes berserk, bursting 3 or 4 rounds. I suspect the heavy buffer and light trigger. 


However with 4 weighs (2 tungsten, 2 steel) it does not feed well, FTE mostly. Pushes the next round into the partially extracted spent case, shoving the bullet of the new round into its case.


What are your thoughts, what weights in the SCS combo are you running or would recommend to try? Looking for maximum reliability.


Thanks in advance!



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I have tried both - I have a 5 weight SCS and a 4 weight one.  I tried them both in the same gun.


I was told by JP guys that either an all 5 steel or all tungsten configuration should work just fine with a JP 3 lbs trigger and Federal ammo.  They mentioned that lack of a firm grip on the rifle may cause the burst issues as well.

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Typically I recommend using the operating system parts, if not the entire firearm, from one manufacturer to avoid issues like this. The cheapest route I would suggest is replacing the trigger with a JP. I can't get my JP triggers to burst. I like that they work as intended. 

In my rifles every weight short stroke SCS works from 5S to 5T and at some pretty crazy power factors both high and low. My preference changes but i'm currently at a 5S with Federal 130's. That's also using a JP bolt. If you like you can look up and compare total weight (bolt+SCS) and estimate where that would be at with your system. 

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I can understand if you want to stick with the Hiperfire and make it work. I've been there.


Try disassembling the Hiperfire.  Have read issues of junk getting in there and messing it up, and also the possibility of a mangled disconnector spring.


If that does not solve the issue, then try to see if you can borrow another buffer system from a friend.

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I have an early HiperFire trigger with the silver springs like you do...  I talked to HiperFire and they sent me an updated pair of green springs and a new hammer spring matched for the green toggle springs... 


Also take the disconnector out and clean all the parts of the trigger...  Make sure the disconnector spring isn't jammed up or bent like @Sniperboy mentioned above.


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Thanks guys, greatly appreciate the advice. I'll take a close look at the Hiperfire and will try the heavier springs.


I think i have a JP AR trigger somewhere, but I do wonder if dropping in a trusty old mil spec trigger would remove the variable of any potential trigger issues? So that I can focus on figuring out if it's the SCS buffer that might be causing problems.  I still can't figure out why I'm having those feeding issues with the 4 weight SCS. 

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If you are not married to the Hiperfire, I am willing to guess a JP trigger will fix your situation.


If not, hopefully one of the fixes will help you.  I have had personal experience or at least a local shooting pal has with the disconnector spring & recoil assembly issue causing the Hiperfire to double.


What is baffling me is your feeding.  In my case I had an issue with jamming only with a longer (short stroked) buffer system, not a shorter one.. seems like you have the reverse? You can try to make your 4 weight system all tungsten?  However, you really have to choose if you want to short stroke or not before you try to play musical chairs needlessly.

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If the trigger isn't doing anything wonky and you've checked out the disconnector spring to make sure it's legit, I kinda doubt it's that, lots of us on here with PCC's run Hiperfires so they're kind of "known quantity", and with the Hiperfire's, the lighter the trigger pull means you're using the heavier springs...


Personally, I've only experienced burst fire when playing with buffer setup stuff, so I know that can do it with some recipes.


It occurred to me that maybe your problem is two-fold or 2 separate issues: Maybe whatever buffer setup recipe you were using where you got burst-fire just also happened to mask a feeding issue because it was cycling lightning fast? And then when you put in a different setup that slowed things down to not burst, a feeding issue was revealed? 


FWIW, I own a Foxtrot Mike upper/lower as a backup w/ a hiperfire and it runs like a watch using traditional buffer setups (works with a .308 carbine spring + 6.5oz buffer + bolt weight in, runs with the .308 spring + 8oz buffer + bolt weight out). That said, the FM lower holds the mags up pretty high (higher than most lowers out there), so I wonder if your lower and upper just aren't getting along?


And just in case, not to be captain obvious, but you did remove the weight out of the FM's bolt right (you're not supposed to run JP SCS setup unless you remove the bolt's weight)..?

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Sniperboy - I didnt get much clarity on the 4 vs 5 issues from JP guys... so i am still as baffled as you.  I am going to try to figure things out with the short stroke 5 weight system and then refocus on the 4 weight SCS.  Maybe upgrade it to a 5 weight slider for PCC or use the 3 weight one and drop it into a 5.56 build.


ck1 -  The New Frontier Arms lower is pretty solid, they make excellent lowers in my experience...  My FM upper has also been pretty good with the 308 rifle spring and buffer in a rifle tube/stock configuration with BCG weight in.  Going to SCS, removing the BCG weight and using the carbine buffer tube is where i ran into these issues.


I also spoke to a couple of friends here at the local club who shoot PCCs with Hiperfire triggers and JP SCSs.  Both of them were strongly leaning towards bump fire due to a weak grip, just as it was suggested by the JP guys from my earlier post.  So i will play with that more.  I also got a set of stronger HF springs to play with. Fingers crossed, this might solve my issues.


Thank you all for the feedback, really appreciate it.

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From Hiperfire troubleshooting page:

4 PROBLEM: Hammer Light Strikes Hammer fall results in light strikes some of the time when using domestic primers but more often on MIL or foreign primers when any of the three toggle spring pairs are installed. The MIL-spec pivot pins supplied with the product are not installed. Instead, the user installs aftermar-ket anti-rotation or anti-walk pins that inhibit free rotation of the hammer in some way because 1) their diameters are greater than 0.154-inches; 2) they do not have a groove to receive the hammer J-spring; 3) they are worn out. REMEDY: Install the FCG with the pins supplied with the product so that the preferred high energy hammer fall is experienced as the baseline. Install other after-market pins only if their impact on perfor-mance does not degrade from the baseline installation.


More related to your problem:


Trouble Shooting Guide For HIPERTOUCH® Series Triggers www.hiperfire.comPage 4 of 7 underside hits the protruding pistol grip’s attachment screw. 3) Debris is in the FCG cavity (small bits of gravel, blown primer cups, shards of cartridge brass, etc.) preventing the trigger from rotating fully for-ward, because of an obstruction along the trigger’s rear underside. REMEDY: 1) Inspect the lower for dimensional compliance and/or substitute an in-spec lower for instal-lation. 2) Replace the over-long grip screw with a shorter one, or file the end back to eliminate the ob-struction and reinstall. 3) Clean out the large scale debris in the lower’s FCG cavity. 8 PROBLEM: Rifle Doubles Occasionally the rifle will “double,” or after a few thousand rounds, it begins to “double.” 1) The lower receiver pivot pin holes’ dimensional spacing may be out of spec on the high side at man-ufacture, or become high due to excessive wear, causing unreliable retention of the hammer by the dis-connector during hammer cocking (see Figure on previous page). 2) The rifle is not gripped securely by the shooter at the pistol grip causing the hammer to reset during rifle recoil and unintended repeat fire when the rifle then rebounds relative to the more or less stationary trigger finger, commonly called “bump fire.” 3) Over time, because the pull weight is light and smooth, the shooter depends less on conscious and deliberate trigger pull and more on reflexive action where the shooter’s muscle memory contracts the pull stroke length (because it can), which in turn leads to inadequate engagement of the hammer’s secondary sear by the semi-auto disconnector sear causing “bump fire.” 4) The rifle “slam fires” because the bolt carrier group is of the “low mass” variety and/or the recoil buffer spring is too stiff causing high energy inertial collision of the firing pin with the cartridge primer. REMEDY: 1) Inspect the lower for dimensional compliance and/or substitute an in-spec lower for instal-lation. 2) and 3) Grip the pistol grip firmly or install a pistol grip that more completely engages the shooter’s shooting hand, especially when shooting over barricades, weak hand, off bipods, or bags to prevent relative motion of the rifle with respect to the trigger finger; and/or do not stop trigger pull at break, but develop the discipline of deliberately pulling through the break to ensure adequate capture of the hammer by the disconnector; and/or increase the trigger pull weight until “bump fire” ceases. 4) Go back to a stock recoil buffer spring and/or employ a standard-mass BCG and/or use ammunition with harder primers to prevent “slam fire.” 9 PROBLEM: Rifle Bursts Occasionally the rifle will “burst” (unintentional repeat fire beyond two rounds). See Rifle Doubles, where all reasons can apply. REMEDY: See Rifle Doubles, where all remedies can apply.





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It now makes sense why they dont recommend the anti walk pins - with a super light hammer spring it needs all the energy and anything that is robbed by the friction on the "locked" pins can cause an issue. Thank you!


I think I have enough info to work out this doubling issue (that may not even be hardware related).  First things to try on my list: a better grip and heavier trigger springs.  Along with the stock Hiperfire pins if i can find them

Edited by nasty618
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  • 10 months later...

Did you resolve the issue?


I'm having the same issue with a Hiperfire Hipertouch Competition trigger in my FM Glock Lower. The trigger worked flawlessly in a CMMG Colt Lower with the same upper receiver, Blitzkrieg 9mm hydraulic buffer, and Sprinco Orange .308 buffer spring.

I tried 2 different upper receivers and 2 different bolts; FM and CMMG.

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