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Head scratcher - my production pistol 130PF load make only 110PF in my JP GMR-15?


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Got a head scratcher here, want to see if anyone have an idea.  Load development for my new JP GMR-15 with 14.5 inch barrel.  Using 3.3gr sport pistol pushing a 147gr bullet, I get 130PF out of my Glock 34, 139PF out of my ruger pcc (16 inch barrel), but only 110PF out of the JP gmr15.  I had 4 loads of sport pistol to try in 0.1gr increments, and consistently see 10 higher pf in my 16 inch ruger (expected) and 20 lower PF in my jp (????) than my 5 inch Glock.  Like, if the Glock makes 125PF, I’d see around 135PF in the ruger pcc, and 105PF out of the JP.  
 

Another person at the range gave me some reloads with n320 powder pushing 147gr and factory Winchester pushing 115gr.  With both of these I get 10- 15 higher pf in both the jp and ruger than the Glock, as expected with the longer barrels.  Somehow it seems it seems like sport pistol powder is the culprit.  
 

How on earth can a 14.5 inch barrel shooting my production rounds designed for Glock 34 at 130PF somehow make 20 lower PF in the JP 14.5 inch, but the same round makes 10 higher PF as expected in the ruger 16 inch?

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My first suspect was chrono issue.  So I took my production match round and chrono it out of my match Glock 34, that I have done many times.  Sure enough it was right at 130PF with good es and sd.  It’s not the chrono.

 

My next suspect was somehow the bullet was not accurate out of the barrel,  going over the chrono inconsistently leading to poor readings.  If this was the case there would be large groupings.  Put up a brand new target behind the chrono at around 10 yards.  It was like a tack driver making almost one hole.  Rifle was very accurate.

 

The other observation was very large variance in speed.  In a 5 shot sample, the Glock was 885fps / es 18 / sd 5.  The ruger pcc was 984fps / es 13 / sd 5.  The jp was 753fps / es 167 / sd 65.  PF out of the jp was as low as 91, for a round that made 130PF in my Glock.

 

I suspect it’s something with pressure development vs timing of the bolt.  Gas / pressure must have been lost from the back somehow.  Hoping someone who really know how the jp system works might have a better explanation to help troubleshoot.

Edited by Galun
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Thats easy.  You're likely using a fast powder that burns up in a short barrel.  It also burns up in the longer barrel,  but the projectile stays in contact with the barrel longer, which starts to slow it down.  I saw similar results with my loads and my GMR15.  My duty rounds were a different story.  The were hotter out of the longer barrel.

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Humm, so it works in the Glock because there is only 5 inches of match barrelZ. It works in the ruger pcc because it’s a cheap loose barrel and the projectile never really slowed down.  It doesn’t work in the jp because it is a high quality tight match barrel so the projectile got slowed down.  That actually make sense.  Whew.

 

Should I up the charge or use a slower powder?  The powder is sport pistol which a lot of pcc shooters seem to use.  But I have some power pistols and long shot that I can try.

 

Maybe load them all to 130pf and find the one with the best recoil impulse / es / sd.

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3 hours ago, RangerTrace said:

Thats easy.  You're likely using a fast powder that burns up in a short barrel.  It also burns up in the longer barrel,  but the projectile stays in contact with the barrel longer, which starts to slow it down.  I saw similar results with my loads and my GMR15.  My duty rounds were a different story.  The were hotter out of the longer barrel.

When I started doing load development for my PCC I read reports of this to people before. IIRC Hi Point (or some other manufacturer) made a video about “load development for a PCC” where they showed a cross section of a barrel that had ~15 Bullets stuck in the barrel stacked against each other. Said its was With a heavy Bullet and slow powder. As Ranger said, it’s because all of the powder gets burnt up, and the bullet is no longer accelerating, but actually decelerating. 
 

in my PCC I never had this problem using coated Bullets, possibly because they have a more slippery surface? But I still only got 5-10pf higher than my 4-5” pistol barrels. 

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7 hours ago, Galun said:

Humm, so it works in the Glock because there is only 5 inches of match barrelZ. It works in the ruger pcc because it’s a cheap loose barrel and the projectile never really slowed down.  It doesn’t work in the jp because it is a high quality tight match barrel so the projectile got slowed down.  That actually make sense.  Whew.

 

Should I up the charge or use a slower powder?  The powder is sport pistol which a lot of pcc shooters seem to use.  But I have some power pistols and long shot that I can try.

 

Maybe load them all to 130pf and find the one with the best recoil impulse / es / sd.

Unfortunately, you probably need a load specifically for for pistols and one for your PCC.  If you have the option, I'd go  light and fast for the PCC to help make the comp work.

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What bullet are you using?  

The coated Blue Bullets 147's under 3.1 grains of Vit N320 run 910 fps out of my 14.5" carbine.

They only run 875-890 fps out of my Sig P320 Legion.  The difference is chalked up to barrel length.

 

BC

 

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I verified al the “slow” cartridges out of the gmr15 with my Glock and they chronoed as expected.  My practice round was 3.3 grains of sport pistol pushing 147gr bullet and it was 130pf.  My load development ladder was 2.8 to 3.2 grains in 0.1 increments.  The pf drop off of these rounds out of my Glock was as expected at around 4 pf per 0.1 grain.  So I know the rounds were not mislabeled and had the correct charge as intended.

 

However, with all the posts, I have a good idea what the culprit was.  I was using xtreme 147gr copper plated round nose which apparently is 0.356 diameter.  Out of the two rounds that chrono as expected in the gmr15, my friends reload was 3.2 grains n320 pushing a 147gr lipstick bullet, and the other was Winchester factory 115gr, both of which I suspect are 0.355.  Billchunn posted his data on a working 147gr load, sure enough blues is 0.355.

 

I am going to do the same ladder (2.8-3.2) with some blue 147gr RN I have, and I suspect they will act normal as expected.  I had also pressed a ladder with Xtreme 147gr 0.356 using sport pistol, power pistol, and long shot, just to see how they work.

 

I was amazed with the accuracy of the rifle despite the inconsistent chrono.  It literally made one hole after 8 Shots at 10 yards.  I think it’s probably the 0.356 diameter grabbing the rifling better.

 

Edited by Galun
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Is this a Labradar style, Magnetospeed or light based chronograph? If the light based, was every bullet shot during identical conditions on the same day within a specified time frame? No wind, no direct sun etc. The reason I ask is I haven't had a load perform as you're describing with any bullet going from pistol to PCC. A 200 fps loss raises a big flag for me. Going from a 5" barrel to my 5.5", 10.5", 14.5" and 16" barrels I've never been more than a couple PF different up or down with a pretty wide variety of bullet weights and sizes. 

I'm not doubting the numbers you saw, I'm just concerned the equipment used may be leading to some pretty significant method error. 

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3 hours ago, Galun said:

Billchunn posted his data on a working 147gr load, sure enough blues is 0.355.

 

Just a little more information.  The velocities that were quoted in the previous post were all obtained from LabRadar chronographs.  The Legion was shot yesterday to get those numbers.  The carbine numbers were from the Ryan Rocks level 2 match in September 2020.

 

BC

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16 hours ago, RangerTrace said:

Thats easy.  You're likely using a fast powder that burns up in a short barrel.  It also burns up in the longer barrel,  but the projectile stays in contact with the barrel longer, which starts to slow it down.  I saw similar results with my loads and my GMR15.  My duty rounds were a different story.  The were hotter out of the longer barrel.

I've had a similar experience.  With light 3.5 loads my H-K VP9 was faster then my JP GMR 13.  With heavier 3.8 loads, the JP was faster.  

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I figured it out.  It’s the bullets, 147 gr 0.356 copper plated Xtreme bullets.  Sport pistol, power pistol, long shot, doesn’t matter what powder.  Huge variance in velocity, extreme spread was 150-200fps.  With long shot powder I even got some at 500fps.

 

Using blue bullets 147gr 0.355, I got expected results.  2.9 gr sport pistol at 1.135oal gave 130PF with 2.3 MOA accuracy.  
 

Using bear creek moly coated 147gr 0.356, I also got expected results.  2.9 gr sport pistol at 1.135oal gave 130PF with 1.46 MOA accuracy.  I think non plated bullets are ok with 0.356 since they are softer than plated.

 

Just for fun, I shot the Xtreme 147gr 0.356 at 50 yards.  Around 7 MOA.  Fliers galore.

Edited by Galun
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On 2/10/2021 at 7:04 PM, Galun said:

Just for fun, I shot the Xtreme 147gr 0.356 at 50 yards.  Around 7 MOA.  Fliers galore.

FWIW I had issues myself with Xtreme bullets.  I normally use Montana Gold or Hornady HAP bullets, but switched to Xtreme due to lack of availability of the others.   At 10 yards I was getting a 12 inch group with my Glock G34, including about 10% flyers.

The short answer is that I was putting too much crimp on the bullets.  Nothing extreme, but enough to distort the thin jacket and compress the bullet to the point that it wasn’t properly grabbing the rifling.  Backed off on the crimp and the rounds performed as expected.

 

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On 2/10/2021 at 6:04 PM, Galun said:

I figured it out.  It’s the bullets, 147 gr 0.356 copper plated Xtreme bullets.  Sport pistol, power pistol, long shot, doesn’t matter what powder.  Huge variance in velocity, extreme spread was 150-200fps.  With long shot powder I even got some at 500fps.

 

Using blue bullets 147gr 0.355, I got expected results.  2.9 gr sport pistol at 1.135oal gave 130PF with 2.3 MOA accuracy.  
 

Using bear creek moly coated 147gr 0.356, I also got expected results.  2.9 gr sport pistol at 1.135oal gave 130PF with 1.46 MOA accuracy.  I think non plated bullets are ok with 0.356 since they are softer than plated.

 

Just for fun, I shot the Xtreme 147gr 0.356 at 50 yards.  Around 7 MOA.  Fliers galore.


Good lord, I stand corrected! Thank you for updating everything as far as the details on the chronos as well. 

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I experienced similar fps reduction in my 9mm loads running Ramshot Competition powder in my Colt6450.  Without getting out of my Lazyboy recliner to look at specific data ....but I posted specific data results in the 9mm reloading area Years ago ..... fast powder in a longer barrel Scrubs fps......if you can not safely use more of your stated powder than switch to a slower powder for a longer burn.

H

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I had similar results with 147's going from my Shadow 2 to JP-15GMR... Although not that extreme. Finally I wenst for plated 124 RN (much flatter also) and changed powder from N320 to RS12 (which is just marginally slower). Now it is as it should the JP being faster then Shadow 2...

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I've got some successful loads with the JP GMR-15 with 14.5" barrel.  All at least 5 shots.  Hopefully this will help others.

 

1.  2.9 gn Sport Pistol / Blue Bullets FP 147 gn / 1.135 OAL => 869 FPS / ES 61 / SD 22 / 128 PF 

2.  2.9 gn Sport Pistol / Bear Creek Supply Moly Coated 147 gn / 1.135 OAL => 878 FPS / ES 23 / SD 8 / 129 PF 

3.  3.5 gn Sport Pistol / Xtreme CPRN (plated) 147 gn / 1.135 OAL => 889 FPS / ES 54 / SD 20 / 131 PF

4.  4.1 gn Sport Pistol / Xtreme CPRN (plated) 115 gn / 1.135 OAL => 1124 FPS / ES 52 / SD 19 / 129 PF

5.  5.0 gn Power Pistol / Xtreme CPRN (plated) 115 gn / 1.135 OAL => 1114 FPS / ES 74 / SD 24 / 128 PF

6.  5.1 gn Long Shot / Xtreme CPRN (plated) 115 gn / 1.135 OAL => 1142 FPS /  ES 88 / SD 30 / 131 PF

 

Going for either faster powder heavy bullet to reduce felt recoil, or slower powder light bullet to work the comp.  Don't know which one I like more yet.  My preference is to use the 3.5 gn sport pistol 147gn plated, and the 5.1 gn long shot 115 gn plated.

 

Shot timer with sensitivity at 13 failed to pick up my 147 gn rounds.  Had to boost sensitivity to over 20.  Will likely have reshoot problems.

 

Om a windy day I had some terrible accuracy problems with my 147 gn loads... like a 10 inch group at 50 yards all to the right of POA.  I think the 147 gn lost too much velocity at 50 yards out.  Probably fine for USPSA but not as a PCC in a multigun match.

Edited by Galun
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Thanks for the info Galun !

 

I recently started working on loads for my MBX 14" PCC. Up to this point I've been content running my handgun loads which is a Blue 135gr TC with Sport Pistol.  I've made the decision to start shooting the PCC more often so I guess it's time to pony up the resources and develop a load for it.

 

I was following another thread on this forum and landed on Power Pistol using it with a 115gr FMJ. Since I have a bigger stash of Sport Pistol, I can see doing some testing with ASP in the not so distant future.  Up to this point, the only real testing I did was compare the accuracy of plated, coated, and jacketed bullets (all 124gr) from the PCC.  The jacketed had the best 25 yard group - not surprising. The issue (today) is sourcing exactly the bullet I want in the quantity i need.  

 

I started by working up from a load I found elsewhere in the BENOS forums. The result is pushing more toward what you are finding; 5gr of PP.  It definitely generates enough noise at the muzzle; a shot timer should have no problem picking it up. The recoil pulse is a little shaky but that's probably a matter of stance/grip technique. 

 

While looking around for information about the PCC recoil pulse, I ran across this article;

 

https://jprifles.com/document_pdfs/PCC Load Development Article.pdf

 

They show some data using some pretty popular powders - they obscure the powder name probably to make their lawyers happy. They also talk a bit about the combo of bullet weight and powder burn rate.

 

 

 

 

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I saw that JP PCC load development article... and at first I had no idea what the powder were.  When I finally saw someone said JP tested longshot, all those names finally clicked for me.  I actually had some of their every single powder!  I was able to replicate almost the exact results, off by 0.1 gn here and there.  It’s an awesome starting point for PCC load development... if I had known earlier I would have saved quite a few laddered loads to find the sweet spot.

 

I didn’t use Titegroup because I read that they run hot and burn up the bullet.  I never liked titegroup in my 5” pistol anyways and I imagine in a 14.5” rifle it will be worse.

 

I really like the feel of sport pistol with a 147gn bullet.  Recoil impulse was almost non existent.  But it makes very little sound, and I think cross wind will have an effect on far shots.  

 

I did compare power pistol and long shot with 115 gn plated bullet.  With power pistol I got sub 5MOA, with long shot I got sub 4 MOA, all at 50 yards.    That’s why I chose long shot.  The recoil impulse of long shot also felt a bit better, like it’s more dragged out?  It would make sense since long shot is the slowest burning powder. But it could also just be in my head.

 

A PCC GM told me to pick the load that gives me the fastest splits at 25 yards with tight A zone hits.  That’s really the ultimate test since everything at shorter distance will only be easier.  This test takes all factors into account... accuracy of the load, recoil impulse, bolt cycle speed, dot movement, etc.  Just pick the load that feels best at 25 yards and go with it.

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