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PCC Doubling - Causes and Cures?


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My brand new JP 9mm doubled and tripled several times on it's first trip to the range.  I swapped out the JP trigger springs for a mil spec set and it works fine.  Trigger is a little bit heavier but it never doubles and breaks like glass.

 

Doug

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10 hours ago, Flatland Shooter said:

interesting.  I agree, Eric does know what he is talking about.

 

How does a 223 carbine spring compare to a 9mm spring?  Is it heavier or lighter?

 

Thanks.

 

Bill

Hello: The 9mm buffer spring is actually a 308 spring. The 223 spring is lighter and the wire is smaller in diameter. I measured a 9mm spring and the 308 carbine spring and they are the same diameter wire and the same compression weight. Thanks, Eric

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Do you think it is a combo of the light trigger & heavy spring/buffer?  Mine is the opposite. I have a Hyperfire EDT trigger which is a little heavier with the Taccom 2pc PCC buffer and their light AR spring and have no problems.

 

Another one of our shooting buddies had the same problem as Bill. He was running a light trigger with a heavy long buffer and spring and it went to double and triple. Changed to the lighter buffer and spring and has no problems.

 

gerritm

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On 4/14/2017 at 8:57 AM, gerritm said:

Do you think it is a combo of the light trigger & heavy spring/buffer?  Mine is the opposite. I have a Hyperfire EDT trigger which is a little heavier with the Taccom 2pc PCC buffer and their light AR spring and have no problems.

 

Another one of our shooting buddies had the same problem as Bill. He was running a light trigger with a heavy long buffer and spring and it went to double and triple. Changed to the lighter buffer and spring and has no problems.

 

gerritm

I think its a possible cause. My gun would burst set up like that. I want to say its caused by all that and bolt/buffer weight slamming rear causing the gun to lurch away from ones trigger finger(causing it to reset) and then slamming into the barrel causing the gun to lurch forward against ones trigger finger. AKA bump fire. I have no proof, just lots of evidence. I just went to a Hiperfire ECL and I think the length of pull and reset help tame that when compared to the light/short triggers I have tried. The Hiperfire has never doubled on me even using bolt/buffler/load combos that would constantly double with an Elf and JP trigger. Both triggers run shorter than the Hiperfire, the Elf is lighter, the JP is heavier . 

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Just a quick update.

 

Made it to the range this afternoon.  Gun was doubling (only happened twice) with the stock 5.2 ounce buffer and 9mm (.308) recoil spring.

 

I added a standard carbine buffer (3.0 ounce) and .223 spring to the mix.  Ran each combination on bill drill six times each (36 rds) to see what happens.  Someone also pointed out that gripping the gun lightly may also contribute to doubling. So I kept a good grip on the gun on all runs.

 

I was unable to get the gun to double with any of the combinations.  The most dot movement was with the light buffer and .223 spring.  The heavy spring with the light buffer was slightly better.  The heavy buffer with the .223 spring reduced the dot movement almost to the same level I was getting with the .308 spring and heavy buffer.

 

Going forward, I'll run the heavy (5.2 ounce) buffer with the lighter (.223) spring.

 

Bill

 

 

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  • 3 months later...
On 4/11/2017 at 7:04 AM, Patrick Scott said:

Yup, exactly why I carry a ALG ACT with JP springs reading to go in my range bag if my Hiperfire fails me.

 

ALG ACT is only thing that won't bump fire on me. It's just much slower trigger. 

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On 4/11/2017 at 7:04 AM, Patrick Scott said:

Yup, exactly why I carry a ALG ACT with JP springs reading to go in my range bag if my Hiperfire fails me.

 

ALG ACT is only thing that won't bump fire on me. It's just much slower trigger. 

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I put a JP trigger in my Quarter Circle 10 PCC a few months back. At my first match it was doubling and tripling a lot for the first few stages. I suspected it was bump firing so I adjusted the stock out a couple of notches (i.e. increased the length of pull about an inch or so). The problem went away for the rest of the match, and the gun has not doubled since.

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2 hours ago, StealthyBlagga said:

I put a JP trigger in my Quarter Circle 10 PCC a few months back. At my first match it was doubling and tripling a lot for the first few stages. I suspected it was bump firing so I adjusted the stock out a couple of notches (i.e. increased the length of pull about an inch or so). The problem went away for the rest of the match, and the gun has not doubled since.

Shooting steel matches with pcc always against shoulder I haven't experienced any doubling. But when trying to shoot and move or really push it, gun goes into burst mode quite easily. I'm running taccom 2-stage buffer and 10% reduced rifle spring. If I go to standard rifle buffer like 2.8oz it hasn't doubled. Chrono'd my ammo and I'm shooting 124s @ 1139 fps for 141pf. Going to try and remove bolt weight and run 6oz buffer with red hammer spring and stock milspec trigger return spring on the JP trigger and see if it won't double. 

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On ‎4‎/‎10‎/‎2017 at 8:48 PM, Flatland Shooter said:

 

I'm not running a heavy spring or buffer.  It got the stock PSA 9mm spring and 9mm buffer (5.2 ounces if I remember right).

 

I do have a buck and a half in change behind the recoil spring but its been in there since the beginning.

 

As for holding it loose, my quest for speed may have resulted in me not keeping a really good grip on the gun.  Aircooled6racer also mentioned this in a PM.

 

Its something I'll watch.

 

Thanks.

 

Bill

 

What advantage are you seeing pre-loading the recoil spring that much?

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My limited experience with the heavier factory 9mm PCC buffer/spring combo (i.e. the spring/buff that came with Lone Wolfe and NFA lower) is they would bump fire sometimes in matches when in hoser mode (a couple time per match). As discussed else where here, some folks like and practice it. I couldn't get it to occur on command very well, though didn't try real hard. When I first installed the JP SCS system with the 110% 308 spring it came with, I still had few bump fires. Lightening the weights in the SCS and using a 100% 223 spring seems to have eliminate it (with mouse fart 115 load). FYI: There was also more felt recoil and dot bounce with the heavier spring/buff combos for me. There's a lot of variables here to ponder.

Edited by littlefish
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6 hours ago, littlefish said:

 

What advantage are you seeing pre-loading the recoil spring that much?

 

It's not for preloading the spring, it's for limiting the bolt's travel. On a gun with LRBHO without the quarters, the bolt can get a running start into the bolt catch and break it. Adding the $1.50 in quarters keeps it from moving more than probably 1/8" behind the bolt catch while still allowing the gun to cycle normally. 

 

Maybe it makes it cycle ever so slightly faster too, but that would be almost totally imperceptible. 

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7 hours ago, littlefish said:

 

What advantage are you seeing pre-loading the recoil spring that much?

 

Goal was not to pre-load the spring but reduce rearward movement of the bolt.  Allowing the bolt to only clear the bolt catch by a little over 1/4" has kept the catch intact. The AR-9 is reported to be tough on bolt catches.

 

OOPS, Xanantos903 has already responded ( and done so better than I did).

Edited by Flatland Shooter
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19 minutes ago, BigBamBoo said:

If you use a machined bolt catch...Seekins is a good choice....it will handle the abuse much better then a standard LPK catch.

 

Did not know these existed.   Added to my wish list.  Will get one and switch it out if and when the original match catch fails.

 

Do you have a link for this part?  The only one I see on the Seekins website if MIM.

Edited by Flatland Shooter
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On 8/13/2017 at 9:01 PM, HoMiE said:

Shooting steel matches with pcc always against shoulder I haven't experienced any doubling. But when trying to shoot and move or really push it, gun goes into burst mode quite easily. I'm running taccom 2-stage buffer and 10% reduced rifle spring. If I go to standard rifle buffer like 2.8oz it hasn't doubled. Chrono'd my ammo and I'm shooting 124s @ 1139 fps for 141pf. Going to try and remove bolt weight and run 6oz buffer with red hammer spring and stock milspec trigger return spring on the JP trigger and see if it won't double. 

Went out and tested JP trigger with red hammer spring and mil spec return spring, could not get gun to double running taccom 2 stage 6oz buffer and reduced rifle spring. Even with a loose grip or shooting while moving I couldn't get it to go into burst mode like I had been experiencing. 

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On ‎8‎/‎16‎/‎2017 at 8:40 PM, Flatland Shooter said:

 

Did not know these existed.   Added to my wish list.  Will get one and switch it out if and when the original match catch fails.

 

Do you have a link for this part?  The only one I see on the Seekins website if MIM.

I've ordered Skeekins catch from Brownells.

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  • 2 weeks later...
On 8/13/2017 at 10:26 PM, ChuckS said:

Watch some of the Max Leograndis videos. He has learned how to control it. Super quick splits when allowable

I could not do it on command and I could not control it when it did bump fire. Sometimes it would be two shots, sometimes it would be 3 or 4. I am finding it harder to shot PCC as fast as I used to shoot an open gun. 

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1 hour ago, HoMiE said:

I could not do it on command and I could not control it when it did bump fire. Sometimes it would be two shots, sometimes it would be 3 or 4. I am finding it harder to shot PCC as fast as I used to shoot an open gun. 

With all the physics of the heavy recip. mass, the PCC will never cycle like a fine tuned open pistol. Perhaps to goal should be to match a fine-tuned 5.56 AR?

 

In any case, it looks like Max may have run into an issue with his technique at Lucas. I was wondering if/when something might come up.

 

 

Edited by ChuckS
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