Problems with failures to feed with Underwood Ammo, Gen 4 Glock 20

[RMM]

David, is there any chance that your new recoil spring is binding when the slide is to the rear?  Reason I ask is that I had my G20 lock back several times with the Wolf 22 lb spring... I think that it may be too long and may need a few coils trimmed from it.  Never had any problems except for with this spring.  The gun didn't jam but it did lock back with rounds left in the mag and I have never had that happen to me shooting this gun or any of my other guns before. I thought that maybe I was riding it with my thumb but it happened a few more times so I swapped out that spring. 

My G20 has run flawless except for with the Wolf 22 lb. spring, with the factory spring I have had no malfunctions shooting Underwood 165 & 180 HP & TMJ, PMC 200 gr., & 40 S&W 180 gr in stock bbl.  I have shot one handed, weak and strong hand, etc. and have had no malfunctions yet (~500 rounds).  My wife shot the gun (she is 5'4") and although she didn't really care for the recoil she also didn't have any malfunctions.

I still think that there is something wrong with your gun, it shouldn't be having problems even with the hotter rounds. 

[DAVIDF]

Maybe, I do seem to actually have more problems with it than with the stock. Plus, this is a Gen 4 I have. I use an adapter sold by Glockstore (that fits in the end of the slide)  to allow the use of a Gen 3 type guide rod. Maybe this is causing some binding as the adapter is thicker (from front to back) than the normal slot at the front of the slide of a Gen 3 or Gen 4. It works perfectly with lighter loads, even the very light American Eagle.

I agree, I think there is something wrong with my particular gun.

[Intercooler]

   Good info and glad I could help. Other than the jamming issues how did you like the PBR?


    Could be your spring setup but I am leaning more towards the mags when you are having slide lock-back problems. Anyone around you have a perfect functioning G20 Gen4 you can swap the mags with? Do you have a light spring you can try? When I went down to an 11lb spring in my Match shooting the hot stuff no change in function.
     It appears ammo isn't really the problem other than the heavy loads are smoking out a pistol issue. If it's every round of the strong stuff I bet mags.

[RMM]

I initially thought mags as well but what are the odds of getting multiple new magazines that have weak springs/are otherwise defective?  Possible but not likely. 

[Intercooler]

[RMM]

My Gen3 G20SF also has the "bump" trigger bar from the Gen4.  No problems (FYI my Gen 4 G17 also has no problems). 

[DM1906]

Interference (internal or external), frame battering or a weak slide catch spring is more likely than the magazine, especially if it happens with more than one mag.  Have a look at the slide stop.  If it looks all beat up, especially on a "new" pistol, it may be an issue with a too light RSA.

The ejector also plays a part.  If it's bent too far down or inward, the loaded rounds will drag along it, then spring up once clear (check the ejected brass for a scratch along the case wall).  The ejector should be parallel with a round in the mag, but not touching with any pressure when the mag is pushed up firmly.  It should also not contact the cover when the slide is installed, although a lot of them do (and Glock says not abnormal).  Every Glock I've had since 1992 required some adjustment.

Also, if you can lock back the slide (obviously, you can), the RSA length shouldn't be an issue.  Remove the spring, reassemble, and pull it back.  Note the stop location (pencil mark helps).  Reinstall the spring and repeat.  It should pull back the same.  If it doesn't, you have an RSA interference.  This is pretty much eliminated as a problem, unless it happens with more than one type of ammo.  The slide distance vs. spring rate just isn't that narrow of a window.  They should (almost) all slide fully.  The only variations are the velocity, and force on contact.  The DE Lite and PRVI rounds might be the exception.  I can only force a "short cycle" with a 24# spring and .40SW rounds (although they've never failed to fire reliably).  I suspect PRVI rounds are lighter than standard .40SW, while the DE Lite's may be close.  American Eagle (the lightest 10mm rounds I've fired) will cycle fully, even with a 24# spring.  If you must see if it is in fact fully cycling, place a smear of grease on each side of the stop, assemble and carefully cycle in a round (without pulling fully rear), and fire.  Disassemble and inspect.  If grease is transfered to the slide, it's fully cycling.  If not, something is holding it short.

[The_Shadow]

I am racking my brain as are you all about the issue DAVIDF is seeing.

Just as the trigger bar adds friction to the trigger pull, it is also dragging on the inside of the slide...however is that the culprit to poor feeding with higher impulse ammo?  I don't think so.  The increased slide velocity is to the rear due to the higher impulse ammo, thus as the slide returns to strip a fresh round, the rear of the cartridge is not sliding up the breech face properly to allow it tip over fully to enter the chamber. 

What are we actually seeing...the slide is accelerated to the rear, dragging the spent case out of the chamber, that case hits the ejector to be knocked off the extractor, then the slide travels further rearward, precocking the striker (this is where that trigger bar would exert the most pressure because of that bump), rebounding via the recoil system to strip the next round from the magazine with the forward momentum.  That round is binding without tipping fully into the chamber...Why?

Is that trigger bar bump pushing the slide over too much to allow rounds to slide into place?
Look for a burr or something on the underside of the slide on the raised section that pushes the fresh round to chamber.
Inspect the breech face for roughness, that could be adding drag to hamper cartridge case from sliding up into place.
Inspect the barrel hood for roughness where the cartridge case rides to the chamber.
With the new cut of the Gen4 for the redesigned recoil System, it there something dragging not letting the barrel to rise up into battery in relation to the locking block?

Anyway these are the things I am running over and over in my brain, thinking of a fix, it could be a dangerous situation!   

ps.  When you place a loaded magazine in the frame, Do you slam it home?  Sharp rap upward with the palm of your hand.
Do you seat all the rounds to the rear of the magazine by rapping the flab back side against the palm of your hand?

[DAVIDF]

Intercooler, accuracy was good with the PBR but not as good as the Underwood. Nothing from a rest so it wasn't a precise test. PBR seems to be using a dirtier burning powder as well. That is not an issue with me, just an observation. Don't know if the accuracy difference is because this barrel does better with TMJ vs other brands FMJ? Was Underwood using Speer TMJ with the Delta Lite? I know the bullet had a different shape than the current 10mm TMJ but I don't know if Speer changed the design slightly. Overall, I think the PBR is excellent especially considering their price.

Also, no one I know owns a Glock 20.

I don't think it is the RSA at least with the stock springs as far as length. Maybe too light with the stock springs. The slide stop spring seems about the same as my other Glocks, but then they are 9mm and have not been subjected to this type of recoil.

No marks on the spent cases from the ejector.

I'll dissasemble today & look at the how the trigger bar is dragging on the inside of the slide. I would guess that is not the issue as this trigger is the best I've felt on any Glock. I'll look at the top of the barrel hood & breech face. I've looked carefully at how the barrel rises up into battery & seems within spec to me.

Magazine is slammed home good. Don't normally rap the back side, but I load it the way I do all my others making sure that the rounds are fully seated to the rear. Under recoil would they stay in that position anyways? The magazine follower on these are not the full length of the magazine like they are with the 9mm. Is this a change from the Gen 3s?

[Intercooler]

   Those were FMJ round nosed as opposed to TMJ's with the flat points. Those are early and what Kevin based the Delta-Lite TMJ's now offered by him. Possibly #9 gives more residue than the 800-X Kevin uses.

[4949shooter]

Kevin offers a Delta lite fmj? I thought it was just Gold Dots..

[DAVIDF]

The Gold Dots is what he has listed now. These were older loads that Intercooler sent me. I talked to Kevein a few weeks back asking him if he could load more of the Delta Elite with whatever bullets he had available. But he seemed reluctant. I guess the max loads sell too well

And, as far as the residue from the PBR loads, wasn't extreme. And, not a lot of residue in my gun. Just more than the other loads. I handload 44 mag with Unique & it works quite well. Unique leaves way more residue than what PBR is using.

[DAVIDF]

I thoroughly cleaned my gun & examined where the trigger bar rubs the frame. Didn't notice any marks, nothing unusual. Slide stop is showing normal wear for the number of rounds. Barrel hood & breech face look very good to an amateur.

[The_Shadow]

DAVIDF, not being there with you to help solve this puzzle makes for speculations...
One other thing I was thinking of is, are the rounds in the magazine sliding forward under the heavier recoil impulse?
Thinking about a cartridge that is already forward as the slide kicks it, that they are standing upward instead of riding up the feed ramp to full chamber.  I would check between shots by pulling the magazine out to inspect after every shot to see. 

[4949shooter]

My G20SF had has similar problems. I am working on tweaking it with springs.

I do think the ammo is part of the problem.