GMR-13 issues

[brian45acp]

I have been running my JP since 2017 at weekly matches and have an estimated 40-50k rounds through it. I could bet money on not having a single malfunction a year on this thing. Well, my luck ran out and its driving me nuts. 

 

So let me try to give a short run down. Started having double feeds and even several jams on the load during make ready from a closed bolt and inserting mag then charging the handle. I narrowed that down to a filthy extractor because I had not actually pulled the roll pin and taken it out in a very long time. So I tossed it and put a new one in and the following match it ran no issues so I figured I found the problem. Match after that the double feeds came back. My next thought was short stroking so I bumped my load and had a good match with no issues. Match after that it started again so I reduced my short stroke SCS by exchanging a tungsten for a stainless so I now have 3 T and 2 S. By the way my load is 124grn jhp and original load I used for a long time chronos at 1050fps on average. New load now is same bullet and 1150 fps on average. My OAL has always been 1.095 and has never changed since I owned the pcc. 

 

People keep suggesting a mag issue but I can't find a thing wrong with it. I am using a OEM 33rnd mag with Goliath extension. Spring seems good and is still same length as a new one. I have de-burred the inside of the mag originally and went through it again just to be sure. That mag has been ran since mid 2019 so its not a new factor to the equation. 

 

Yesterday's match first stage 10 rounds in it double fed again. My rifle is detail cleaned before each match and I oil the piss out of the bolt contact points. After that jam I switched to a brand new mag same setup with a Goliath extension and had no more issues during the course of fire. I did have a classifier where I used my carry optics g17 mag and it jammed on the load during make ready again. I dont have bolt lock back so this occurs on a closed bolt and after inserting the mag I crank the handle. These jams seem to nose dive so I pull the charge handle back and rotate the ejection port down and shake the round out. Seems to be the same sort of jam during course of fire also and thats how I clear them. Its always a live round and not spent brass getting stuck. 

 

I have replaced all the O rings on the SCS and the recoil spring. I have a new extractor in place and I have inspected all the parts for damage etc. I put the safety on and hand cycled a full 50 round mag trying to short stroke it and do different things to induce the issue but it feeds perfectly. 

 

I am going to call JP and get some help but I have tried everything there is and can't figure this out. People say use different bullets etc but after this many rounds its not going to suddenly be the bullet profile or type of mag I am using. Despite me not being able to see anything wrong with the mag I am going to keep running the brand new one and see if it has issues. Because I had jams on the regular g17 mags while loading I am confident its not a mag or spring issue. 

 

Is mag spring length a good indicator of weakness or not? It feels the same as the new mag and is exactly the same length and not even 1 coil shorter. 

[jnr88]

I don’t shoot the JP but it has a reputation for reliability. If it shot fine why would you introduce new variables as you troubleshoot. This seems to be a very risky road. I suggest shooting the gun in the same configuration that ran reliably for years as you do maintenance items. JMO

[brian45acp]

I didnt change anything and started having issues suddenly. This is what is driving me nuts because I felt I was way past needing to dial anything in. I never had issues and stayed with what worked. But now there is something wrong so I am having to figure it out. 

[philmadxx]

I would think the nose dive issue is mag related.  Most of the mag extension manufacturers say that you can get a bad mag from the factory and to try several if there are issues.  I had issues with my GMR and the Goliath related to the OAL of the ammo but you're running stuff well within spec. 

Maybe try the Glock mags without extensions to see if there are issues.  

Good luck.  

[brian45acp]

Unless this mag suddenly went bad in about a year and a half then I dont know why it would suddenly be the problem but I do agree it seems mag related. I measured the feed lips and they are the same as a new mag. I inspected the heck out of it and can't see anything either. But running the new mag a few matches will tell the story I suppose. 

 

I like to figure things out and learn so this I dont like this. Just to write something off as mag related and not understand or see the issue doesn't satisfy my understanding of the issue. 

[brian45acp]

I’m going to reduce buffer weight and send it next Saturday and see what happens. All that makes sense to me is short stroke causing the round to get stuck. 
 

I will report back and hope it helps others 

[LowSpeedHighDrag]

59 minutes ago, brian45acp said:

I’m going to reduce buffer weight and send it next Saturday and see what happens. All that makes sense to me is short stroke causing the round to get stuck. 
 

I will report back and hope it helps others 

Did you make any changes just prior to the problems?

 

With a high round count I would look at wear and tear as an issue.  Possibly it’s time for a new bolt?

 

[brian45acp]

No new changes for about 10k or more rounds I would say. 
 

I was wondering about high mileage wear and tear. How would the bolt wear out? Looking at it I can’t seen anything but it would be logical that all these parts have a life expectancy.

[philmadxx]

If it has run perfectly for thousands of rounds with X buffer weight, why would it all of the sudden need to be changed?  Mine runs with 0 tungsten, 5 steel, 1 and 4, 2 and 3 and 3 and 2 - no failures - although some changes in recoil impulse.  Mags do go bad from time to time (I hear, can't say it has happened to me).  

[Bdh821]

Try Glock MBX steel mags?  Check trigger components to see if your disco is broken?   Change the buffer recoil spring?  Change mag springs? Check your extractor spring or extractor itself?  check the mag feed lips?  check anything that is a wear item even if it doesn't make sense that they're related.  As you said, nothings changed other than it stopped working after a ton of rounds.  

[TRUBL]

Glock magazines do NOT double feed!!!

If you've started to have problems.......look at 1911 101......it's most likely going to be extractor, ejector position or recoil spring. OR.....you have a magazine that went bad.

 

I believe when you say double feed......you actually that mmmmmmmmmaybe a spent round did not clear the firearm? But it still cycled enough to try to feed another round out of the magazine (1911 101). OR the firearm misfed and you tried to charge the weapon again (possible bad mag).

 

To say that a Glock magazine has double fed......would literally mean that upon trying to charge the weapon....TWO ROUNDS CAME OUT OF THE MAGAZINE AT ONCE!!!!.....Did that happen? I'm gonna say NO.....if it did.....end of story, your magazine is bad.

Edited January 18, 2021 by TRUBL

[brian45acp]

1 hour ago, TRUBL said:

Glock magazines do NOT double feed!!!

If you've started to have problems.......look at 1911 101......it's most likely going to be extractor, ejector position or recoil spring. OR.....you have a magazine that went bad.

 

I believe when you say double feed......you actually that mmmmmmmmmaybe a spent round did not clear the firearm? But it still cycled enough to try to feed another round out of the magazine (1911 101). OR the firearm misfed and you tried to charge the weapon again (possible bad mag).

 

To say that a Glock magazine has double fed......would literally mean that upon trying to charge the weapon....TWO ROUNDS CAME OUT OF THE MAGAZINE AT ONCE!!!!.....Did that happen? I'm gonna say NO.....if it did.....end of story, your magazine is bad.

Mag issue makes a lot of sense. 2 rounds didn’t come out at once. One round never made it into the chamber and got pinched between bolt face and breech face/barrel.

 

I never saw a spent casing stuck and it’s always a live round. Extractor was changed to new 2 weeks ago. Checked ejector position and it has never moved. Ejector looks the same as my 2nd brand new GMR. The recoil spring was changed 2 weeks ago as well.

 

this crap is driving me nuts 

[brian45acp]

2 hours ago, Bdh821 said:

Try Glock MBX steel mags?  Check trigger components to see if your disco is broken?   Change the buffer recoil spring?  Change mag springs? Check your extractor spring or extractor itself?  check the mag feed lips?  check anything that is a wear item even if it doesn't make sense that they're related.  As you said, nothings changed other than it stopped working after a ton of rounds.  

Looked hard at those mags but I live in the communist state. 
 

Trigger issues wouldn’t cause misfeeds would they? 

Edited January 18, 2021 by brian45acp

[brian45acp]

Called JP and we can’t figure it out either. I’m going to put my buffer system back to what it was and start over. If I change 1 thing at a time I should figure this out. 
 

One thing I didn’t think of is they mentioned reducing weight and increasing charge of my ammo could cause bolt to hit limiter and bounce which would induce feeding issues. The timing would be off and cause problems. 
 

maybe it’s possible as I changed my load and SCS weights I created more of an issue. The original problem for sure was a filthy extractor that was all caked up. But once I changed it and still had a failure maybe something was wrong with a particular round and not something bigger. But my changing things sent me down the wrong path.

[72stick]

If it were my gun, I'd look at the ejector finger and see if the set screws came loose. JP had issues with the early GMR-13 ejectors coming loose. It makes the gun do exactly what you describe. The fix was a new ejector finger with chamfered set screw holes and mild steel set screws instead of the SS set screws. Then assemble with lots of lock tight on both the treads and on the side of the ejector where it mates with the receiver. 

[brian45acp]

2 hours ago, 72stick said:

If it were my gun, I'd look at the ejector finger and see if the set screws came loose. JP had issues with the early GMR-13 ejectors coming loose. It makes the gun do exactly what you describe. The fix was a new ejector finger with chamfered set screw holes and mild steel set screws instead of the SS set screws. Then assemble with lots of lock tight on both the treads and on the side of the ejector where it mates with the receiver. 

I checked those. No presence of rubbing of the ejector on the bolt. No wear marks on ejector top or underside of bolt. 
 

I’ll check them again. I didn’t actually wrench on them. I did pull on the ejector and tap it and checked for movement or signs of rubbing.

[egd5]

6 hours ago, brian45acp said:

One round never made it into the chamber and got pinched between bolt face and breech face/barrel.

Maybe you've checked this, but..

Load a mag up then push each round out like it would be stripped into the chamber. I had a mag or two that had a somewhat sharp edge at the front of the mag. As a round would come out the lip/edge of the case would slightly catch on that. Maybe a round just didn't get taper crimped quite enough or something. Anyway, I slightly champfered/rouded that edge of the mag and it hasn't happened since. Worth a look see. Good luck.

[brian45acp]

1 hour ago, egd5 said:

Maybe you've checked this, but..

Load a mag up then push each round out like it would be stripped into the chamber. I had a mag or two that had a somewhat sharp edge at the front of the mag. As a round would come out the lip/edge of the case would slightly catch on that. Maybe a round just didn't get taper crimped quite enough or something. Anyway, I slightly champfered/rouded that edge of the mag and it hasn't happened since. Worth a look see. Good luck.

I loaded a mag and stripped them one by one by hand and in the rifle. 
 

eventually I’ll figure this out and report back so it helps others. This has to be a good one because it sure isn’t obvious what’s wrong. 

[arcsign]

So... Disclaimer, I’m not a pcc guy (yet), just been spending a lot of time thinking about buffers and stuff on my Grendel AR. 
 

 

There are (at least) two ways to get a double feed (that are bolt/buffer related):

 

- the bolt is too slow and doesn’t manage to extract the first round before closing

 

- the bolt is too fast and ends up catching the case again on the way forward.

 

 

My reasoning goes like this:

 

 - you started with a dirty extractor, and went to a higher charge to compensate, so the bolt got faster

 

- cleaned the extractor, making the bolt too fast to clear... maybe bouncing off the back of the tube/buffer if the action/recoil/buffer spring was worn out

 

- replaced the spring, which maybe prevented it from actually hitting the end of the tube, but new springs have more oomph going forward, and not much difference resisting the initial impulse... so no change really there

 

- lightened the weight of buffer, which made the carrier even faster in both directions

 

 

So... maybe you need to slow it down again, but probably need it slower than you had it originally due to springier spring. (Maybe, my knowledge of springy thingies is less than extensive.)

I’d say go up a step past the original buffer configuration in weight, and that might slow it down enough to not catch the spent case on the return stroke.

 

(Alternatively, if your double feeds leave the spent case in the chamber in front of new round, instead of between the bolt face and the new round, the same change should prevent the extractor from moving as fast during initial impulse and yanking the extractor off the rim of the case... I’m not sure that is as common on a blowback pcc, though, since that can sometimes involves a timing issue where the case is still being held in the chamber by expansion when the bolt starts to move back...)

 

 

[brian45acp]

3 hours ago, arcsign said:

So... Disclaimer, I’m not a pcc guy (yet), just been spending a lot of time thinking about buffers and stuff on my Grendel AR. 
 

 

There are (at least) two ways to get a double feed (that are bolt/buffer related):

 

- the bolt is too slow and doesn’t manage to extract the first round before closing

 

- the bolt is too fast and ends up catching the case again on the way forward.

 

 

My reasoning goes like this:

 

 - you started with a dirty extractor, and went to a higher charge to compensate, so the bolt got faster

 

- cleaned the extractor, making the bolt too fast to clear... maybe bouncing off the back of the tube/buffer if the action/recoil/buffer spring was worn out

 

- replaced the spring, which maybe prevented it from actually hitting the end of the tube, but new springs have more oomph going forward, and not much difference resisting the initial impulse... so no change really there

 

- lightened the weight of buffer, which made the carrier even faster in both directions

 

 

So... maybe you need to slow it down again, but probably need it slower than you had it originally due to springier spring. (Maybe, my knowledge of springy thingies is less than extensive.)

I’d say go up a step past the original buffer configuration in weight, and that might slow it down enough to not catch the spent case on the return stroke.

 

(Alternatively, if your double feeds leave the spent case in the chamber in front of new round, instead of between the bolt face and the new round, the same change should prevent the extractor from moving as fast during initial impulse and yanking the extractor off the rim of the case... I’m not sure that is as common on a blowback pcc, though, since that can sometimes involves a timing issue where the case is still being held in the chamber by expansion when the bolt starts to move back...)

 

 

 

 

This makes the most sense. After JP mentioned issues with too fast of a bolt I started thinking along the same lines. Additionally I switched to a very slick light grease from bore tech so I think that increased the bolt speed as well. So the extractor issue was diagnosed after I started thinking it was a cold weather and not enough lube issue which is when I switched to the grease.  

 

I think you may be on to something that makes the most sense to me. I will put the weight back to what it was and see what happens. 

 

I never had issue with spent case so that last part doesn't apply so much. I also dropped a quarter in the buffer tube to preload the SCS assembly to help keep the bolt closed a smidge longer. I have always done that since I got the rifle and I think it helps. 

Edited January 20, 2021 by brian45acp

[NOSHMJ]

I had a very similar issue.  New mag and problem solved.  I was using a glock mag with MBX extension.  I change to new mags and springs every season now because I learned the hard way.  Take a new mag spring and compare it to your old one and I bet you will see a difference in length from compression. 

[brian45acp]

17 hours ago, NOSHMJ said:

I had a very similar issue.  New mag and problem solved.  I was using a glock mag with MBX extension.  I change to new mags and springs every season now because I learned the hard way.  Take a new mag spring and compare it to your old one and I bet you will see a difference in length from compression. 

Thats the odd part. The springs are nearly the same and not even half a coil difference. But I have inspected the s#!t out of this gun and it can't be the gun. I ran the potential bad mag yesterday just in practice which is 51 rounds. I shot it off my shoulder and from low ready etc just to see if my issues were from a weak shouldering etc. The mag might just be bad for reasons I can't explain but running the new mag for a while will tell me if thats the case of not.

 

I returned my buffer back to the way I had it with 4T and 1S but but I did bump my load so my 124grn jhp are doing average 1150fps

[gdcguns]

Could it be a burr/sharp edge  on the extractor? It’s a 1911 style extractor, right?  If you have some small files you can try to radius the bottom inside corner of the extractor. That may help. If it’s too sharp, sometimes this will prevent rounds from feeding properly because they can’t slide up behind it. Like TRUBL said, 1911-101.  JMO. 

[brian45acp]

Just want to update everyone in hopes it might help. I put the gun back to the way I had it in terms of buffer setup and started over. It has ran thousands of rounds no issues so it didnt make sense to chase ammo or setup combos. I used a brand new mag with a new Goliath extension which was my back up mag to the same combo which was used the past 2 years. I had 2 matches with not a single problem and I can feel feeding being more smooth. No more noises of bolt to closing then springing shut when moving port to port like before. 

 

Next step will be a new spring in my original mag and run it some more to narrow down the issue. But for sure its with the mag and not the gun. Now the next mission is what part of the mag is giving me issues. I suspect spring length has nothing to do with spring "health". It  must be fatigued and tossing round out of the feed lips during recoil which is why my jams are always a live round pinched between bolt and chamber. 

[egd5]

Since you mentioned the goliath, what is your oal. They recommend no longer than 1.125, I run 1.120. Also did you de-burr the internal of the mag where it meets the goliath? TF has a video I believe about that.