Howard

What causes double feeds? (Glock)

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Shot a USPSA match this past weekend an my always reliable Glock 35 was having three to five double feeds every stage.  Yes I changed something, the ammo.  So I am fairly certain it was the ammo that was the cause, but what was the ammo doing or not doing that caused this.  The OAL of the ammo was the same as my normal ammo.  The only visual difference seemed to be that the bullet tapered from the case to the tip a little more than what I have normally been using.

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Doubt it was the magazines as they are Glock magazines that all ran fine the week before and had the problem with all of the magazines that day.  The ammo was from Peakperformanceammo.com and they use 180gr FP Berry Bullets.  These were recommended to me by a competitor at a local match a few weeks ago so I thought I would give them a try.  I contacted the company and they have not had any other reported issues.  Seems very strange.

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I’m sorry Howard, i’m confused...

Did you get two live rounds, one in the chamber and right one behind it?

Or one live and one spent?

What do the rounds left in the mag look like? Does the top round look like it took a nosedive into the mag or is it sitting normally?

When was the last time you did any preventative maintenance? 

Changed springs?

Inspected the extractor?

Approximately how many rounds do you have through the gun?

Yes, you only changed the ammo, but maybe it ran a little hotter, or maybe a little weaker, and you are now seeing some indications of a weak recoil spring assembly or mag spring.

 

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It is not possible for a live round to chamber and the next one to feed behind it.

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Might not be possible but it happened about 15 to 20 times.

The recoil spring might be too light for that ammo. I had been using some ammo that was about 170 power factor and this ammo is a little hotter. I have a 9mm recoil spring in the Gun (gen4). Maybe I’ll try the stiffer .40 cal spring with this ammo and see if the problem goes away.

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In order for the round to feed, it must be stripped from the magazine by the slide. Once the slide travels forward to chamber the round, no way can the next round inline rise, unless the slide retracts again. Of course, you know that. Good luck.

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13 minutes ago, PK90 said:

In order for the round to feed, it must be stripped from the magazine by the slide. Once the slide travels forward to chamber the round, no way can the next round inline rise, unless the slide retracts again. Of course, you know that. Good luck.

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Only way I can see this.. worn recoil spring.. bent back ejector.. clapped out extractor and loose lips on mags. 

Spent brass catching next round.. but way out of battery. Then slide picks up second round.

dunno, gun is going too far back me thinks 

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Are you getting a malfunction and then manipulating the slide in an attempt to clear it first, and then ending up with a double feed with two live rounds?

Did you keep any of the rounds that this happened too?

Where the two rounds inline with each other ie: The nose of the second round up against the rear of the case that’s in the chamber?

Or was one in the chamber and the other all jumbled in there?

In my experience, two live rounds in the chamber is almost exclusively a magazine issue.... 

 

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9 hours ago, Howard said:

These were recommended to me by a competitor at a local match a few weeks ago

Well THAT is why...! ;)

Sorry, nothing constructive to add.  I read the quoted bit  and thought there is no better way to gain an advantage over someone, short of giving them ammo that jams the gun up so badly that you have to throw it over a wall a couple times...

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Are you getting a malfunction and then manipulating the slide in an attempt to clear it first, and then ending up with a double feed with two live rounds?
Did you keep any of the rounds that this happened too?
Where the two rounds inline with each other ie: The nose of the second round up against the rear of the case that’s in the chamber?
Or was one in the chamber and the other all jumbled in there?
In my experience, two live rounds in the chamber is almost exclusively a magazine issue.... 
 

No did not save any of the rounds, just worked as fast as possible to clear and get back on target. Typically one round was in chamber and another was just lose behind it. Don’t recall where the nose was exactly. Most times I pulled the slide back a little and dumped the extra round out and let the slide go forward on the round in the chamber. Other times dropped the mag and rack out the round.

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10 hours ago, RichP said:

Check your ejector - Its possible for a fired case to strip a round out of the magazine if it doesn't get ejected, and then another gets stripped by the slide.

What exactly would I be looking for with the ejector that might be causing this?

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11 hours ago, RichP said:

Check your ejector - Its possible for a fired case to strip a round out of the magazine if it doesn't get ejected, and then another gets stripped by the slide.

If there's a round still in the chamber it would be the extractor not ejector.  A broken ejector usually will induce a stovepipe malfunction. 

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1 minute ago, GRIZ said:

If there's a round still in the chamber it would be the extractor not ejector.  A broken ejector usually will induce a stovepipe malfunction. 

He said that its a loaded round in the chamber, meaning that the extractor is at least removing the spent case.

While admittedly just a wild guess, if the ejector is bent or broken, it is feasible that the spent casing can be doing some wacky things if not tossed-away from the breech. Other than that, many ammo reloaders have a been known to undersize 40S&W brass to remove any Glock bulge and to make them feed better into match chambers. This undersizing could be causing some issue in how it is being released from the mags.

I tend to agree with HE on magazine issue as well, but you are saying that this is happening across multiple factory mags, so it has to tabled until everything else is checked-out.

What I would do in this situation?,I would restore all of the parts to OEM (making sure that they are all in good condition) and see if that helps.

If yes, then add the non-OEM parts one-by-one to see where the problem lies.

If no, then let the ammo manufacturer know that there is a problem or switch to another company.

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22 minutes ago, RichP said:

He said that its a loaded round in the chamber, meaning that the extractor is at least removing the spent case.

While admittedly just a wild guess, if the ejector is bent or broken, it is feasible that the spent casing can be doing some wacky things if not tossed-away from the breech. Other than that, many ammo reloaders have a been known to undersize 40S&W brass to remove any Glock bulge and to make them feed better into match chambers. This undersizing could be causing some issue in how it is being released from the mags.

I tend to agree with HE on magazine issue as well, but you are saying that this is happening across multiple factory mags, so it has to tabled until everything else is checked-out.

What I would do in this situation?,I would restore all of the parts to OEM (making sure that they are all in good condition) and see if that helps.

If yes, then add the non-OEM parts one-by-one to see where the problem lies.

If no, then let the ammo manufacturer know that there is a problem or switch to another company.

I've seen a lot of guns that ran fine with a broken ejector.  Can't say if a Glock will as I've never seen one with a broken ejector.  However I agree it should be checked.

@Howard if your gun runs fine with all the other ammo you use this had to be an ammo problem a's @RichP speculates.

Get out your calipers or micrometer.  40 S&W (according to the Lyman manual) should be.423" at the case mouth, .424" just forward of the extractor groove, and .424" at the case head.  If  undersized I'd take this up with the ammo manufacturer.

Howard, is that recoil spring "extra power" or "soft"?

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@GRIZ The recoil spring is under powered.  I was using ammo that just made power factor so a while ago I took out the stock recoil unit and installed a 9mm one (yes on Gen4 unlike Gen3 there is a difference).  The gun has worked fine with that.  The only thing that changed is the ammo.  I wish I knew where my cailpers were :(  We moved to FL in June and are in rented quarters right now and I have dozens of boxes that I have yet to open.  If all goes well we will be in our new home in about a month and will start actually unpacking all those boxes.  Till then I think I will just try my normal ammo and hopefully the problem will go away.

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Two live rounds indicates that the second round is somehow jumping out of the mag during feeding. If it weren't a Glock mag, I would suggest issue with the feed lips, however, I highly doubt that. Could also be mag springs.

Could be mag springs combined with the slower cyclical time of the slide due to the weaker recoil spring. If the mag springs are weak that could combine with the slightly higher recoil to spit a round out.

If none of the above, trash ammo.

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@Howard try putting the stock recoil spring back.  It looks like you've been getting away running a softer spring until now.

Is this new ammo softer or standard?

A softer recoil spring makes the slide come back harder than a stock spring.  This puts more wear and tear on your gun.  It also makes your slide come back into battery slower.

I don't think your magazine springs are bad.  I think they're performing as they are supposed to.  By using a softer spring the timing of your gun is screwed up.  Engineers figure out what weight springs to use to get the gun to work reliably.  There is a balance here that you've upset with that softer spring.

I'm speculating what's happening is this new ammo is loaded to standard pressures and running the slide back harder than it was designed to be. The magazine, assisted by the extra hard whack of the slide when it comes back and extra time it stays back, is letting two rounds out instead of one.  If the mag spring was soft it would have a hard time pushing one round up.

The major function of a recoil spring is to return the slide to battery and chamber a fresh round.  That's it.  When one does something to change the parameters the gun was designed to do this in there can be problems.

Many put in an extra power spring in the belief it will help them shooting +P ammo.  See the first sentence of my preceding paragraph.  Now +P does make sense in ammo that is underloaded from the factory like 38 special.  However a semiautomatic pistol is designed to work within a certain pressure range.  Shooting a softer recoil spring slows down the return of the slide and a heavier one speeds it up and slams the slide back harder than it was designed to be.

My idea of +P 9mm is called 357 SIG. A 10mm is a +P 40 S&W to me.

How much of this new ammo do you have?  We need to get your gun working so at least you can use it up.

 

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I agree it is likely the lighter recoil spring which I have used for ammo that just makes power factor, the gun was more reliable with it than the stock spring.  This ammo is a little hotter, so very likely you are on to something.  Will try it both with my regular ammo and with this new ammo with the stock spring.  Thanks.

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