View Full Version : What are the causes of a double feed
Ok I'm mystified as to what can cause a double feed. My wife was having them towards the end of the day today. Here is the scenario
Colt 6920 (the bolt is not colt, but the carrier and everything else is)
Total shots fired: 146 rounds
Magazines: US GI 30 and 20 round types
Shooting positions used: Sitting, prone (both with 20 round magazines) standing (with 30 round magazines)(magazines were never used as a monopod)
Federal XM193...no problems all day
Georgia Arms 55gr FMJ - that's when the double feed problems occurred.
Now I have experienced the same problem when using GA in the past and am inferring that its the GA ammo. My question though is why? What would be wrong with the ammo that would be causing this.
Please explain what you mean by double feed. If you mean 2 live rounds attempting to feed at the same time then it is magazine related. More than likely the magazine spring is worn. 20 rd mags aren't know for being the most reliable.
Failure2Stop
10-05-08, 10:00
"Double-feed" is a very general category.
A true double feed is a magazine or operator fault where the rifle attempts to feed two live rounds simultanously. Magazine issue is generally spread feed-lips. Operator error is usually slapping the magazine dunring seating, causing a cartridge to pop free of the mag, the other is when a initial make-ready fails to feed/chamber and the user re-cycles the CH with the mis-fed cartridge in the upper.
You can also have a dropped extraction where the fired cartridge is still in the chamber when the gun cycles, resulting in a live round hitting the base of a fired round in the chamber. This issue is addressed through the well-covered extractor fixes.
Failure to eject ia also a possibility, where the spent cartridge is still attached to the bolt face when the gun cycles, resulting in the attempt to feed a live and a spent cartridge. Issues with this are ejector/extractor related.
Robb Jensen
10-05-08, 10:13
Double feed as in two live rounds:
As already said slamming mag too hard into gun
Bad magazine
Double feed as in an empty and a live round caught in upper:
Short stroking, causes:
Too weak of ammo, not enough lube, too strong a buffer spring and/or too heavy of a buffer, too much extractor tension, gas leak or running too many CAR 'fixes' as in using a LMT enhanced carrier (the one with the larger expansion chamber) in a gun that it won't work (like a LMT 10" upper).
CarlosDJackal
10-05-08, 10:38
Another cause if a "double-feed" is one where a live round is trying to occupy the same space as a spent cartridge that was not extracted (FTE). Then you have an extractor issue unless the rim of the spent cartridge was ripped off by the extractor. In that case you might have a chamber issue that is causing the case to stick (i.e. Laquer from Wolf ammo, rough chamber, etc.).
Good luck!!
Thank guys. What she experienced was two live rounds trying to be fed at the same time. I did ask her if she was slapping the magazine at all, she said no. I had her demonstrate to me how she was loading the magazines and yeah, shes not slapping them. Ergo why I'm completely baffled. Like I said, this only happened with the GA ammo, not the federal.
Robb Jensen
10-05-08, 10:52
Thank guys. What she experienced was two live rounds trying to be fed at the same time. I did ask her if she was slapping the magazine at all, she said no. I had her demonstrate to me how she was loading the magazines and yeah, shes not slapping them. Ergo why I'm completely baffled. Like I said, this only happened with the GA ammo, not the federal.
The ammo is sized wrong, weak and/or you have a borderline bad magazine. She could be allowing the gun to move too much have her try a more aggressive stance.
When you say 2 rounds try to feed......
Do you mean one it going into the chamber and the other gets caught in the upper and jammed into the gas key?
BravoCompanyUSA
10-05-08, 11:34
As stated above; 99% of the time a Double Feed (2 live rounds trying to be chambered at the same time) is a magazine issue.
The ammo is sized wrong, weak and/or you have a borderline bad magazine. She could be allowing the gun to move too much have her try a more aggressive stance.
Thanks. Her stance wasn't bad, but it wasn't great either. So that is something I worked with her last night.
When you say 2 rounds try to feed......
Do you mean one it going into the chamber and the other gets caught in the upper and jammed into the gas key?
Once round gets partially fed into the chamber, the second one follows it and gets the bullet portion wedged between the bottom of the top round and the top of the chamber / ramp. This is an illustration I just whipped up that shows whats happening.
http://img.photobucket.com/albums/v234/frontline_01/firearms/doublefeed.jpg
As stated above; 99% of the time a Double Feed (2 live rounds trying to be chambered at the same time) is a magazine issue.
Normally I'd agree with you but this one has me stumped. Only the one type of ammo double feeds. Its got me scratching my head unless it is the ammo.
Thanks. Her stance wasn't bad, but it wasn't great either. So that is something I worked with her last night.
Once round gets partially fed into the chamber, the second one follows it and gets the bullet portion wedged between the bottom of the top round and the top of the chamber / ramp. This is an illustration I just whipped up that shows whats happening.
http://img.photobucket.com/albums/v234/frontline_01/firearms/doublefeed.jpg
Normally I'd agree with you but this one has me stumped. Only the one type of ammo double feeds. Its got me scratching my head unless it is the ammo.
I've not had that type of double, but that's better than the type where the round gets jammed in the gas tube.
Either way I'd say it's the mag 99% of the time like others have said. But to have one type of ammo do it and another not sure is different. I'd go with measuring the ammo like has been posted......
How about this. Go to the local gun store, find a PMAG for about 15.00, buy it and see if it continues.
Mark/number all of your magazines so that you can ensure that it really is just the one type of ammo.
If you can take the same magazine, as verified by numbering, and get a DF with the GA ammo but feed fine with known quality ammo, and can get a DF in multiple magazines with the GA but feed fine with known quality ammo, then I'm stumped.
:eek:
Sometimes it's just bad juju. I'm sure there's a scientific/mechanical/chemical/otherwise logical and rational explanation, but I really can't think of a reason for the type of double you describe that would be ammo related.
Just think about what's happening. I'm assuming she's able to chamber and fire the first round just fine, and it's the second (or subsequent) round that's causing the double. In that case you're getting two bullets looking for the same hole. The only way for that to happen is for two bullets to be getting stripped out of the magazine.
Now go look at a loaded good condition magazine. How the hell do you get two rounds out of that badboy at one time?
When you say "US GI 30 and 20 round types", we're not talking surplus are we? We're talking magazines from D&H or similar that you bought NIW, right?
Mark/number all of your magazines so that you can ensure that it really is just the one type of ammo.
If you can take the same magazine, as verified by numbering, and get a DF with the GA ammo but feed fine with known quality ammo, and can get a DF in multiple magazines with the GA but feed fine with known quality ammo, then I'm stumped.
:eek:
Sometimes it's just bad juju. I'm sure there's a scientific/mechanical/chemical/otherwise logical and rational explanation, but I really can't think of a reason for the type of double you describe that would be ammo related.
Just think about what's happening. I'm assuming she's able to chamber and fire the first round just fine, and it's the second (or subsequent) round that's causing the double. In that case you're getting two bullets looking for the same hole. The only way for that to happen is for two bullets to be getting stripped out of the magazine.
Now go look at a loaded good condition magazine. How the hell do you get two rounds out of that badboy at one time?
When you say "US GI 30 and 20 round types", we're not talking surplus are we? We're talking magazines from D&H or similar that you bought NIW, right?
For the magazines the three 30 round magazines were bought within the last 9 months and have either the green magpull follower or the gray one from Anvil Arms. Of the 20 round magazines, I had to borrow them, but they appear on inspection to be in good condition and are relatively new looking. When I spoke to the guys who lent them to her they said that they didn't have any problems to report. As she reported to me, once she switched to the GA, that's when the problems started, regardless of the magazine used. Trust me, I'm stumped too.
you're definitely going to have to get out and test this one yourself.
RAM Engineer
10-06-08, 09:36
...either the green magpull follower...
Did Magpul followers ever come in green? :confused:
TriumphRat675
10-18-08, 16:46
Did the bolt damage the lower round at all? I'm having a similar problem with a close to brand new 6920 and would appreciate any advice.
The gun is somewhat dirty - approximately 400 rounds without cleaning, other than wiping the carbon off the bolt and bolt carrier. the gun was well lubricated and I was using P-mags and 62 grain green-tip ammo from ammo-man. the double feed (two live rounds trying to feed together) happened twice, once with a 30 round p-mag and (i believe) once with a 20 round p-mag. both mags are new and have had been used once or twice with no problems.
both times in my gun, the bolt lugs dug deeply into the round just south of the case shoulder. i've fired about 600 rounds of this particular batch of ammo with no problems in this and an S&W M&P 15, but knowing where it came from i'm not going to absolve the ammo yet...
I'm having the same issue with close to new CMMG middy 16" (mostly PP ammo)...attempting to double feed and also failures to eject, then the next round jams into the spent case. Once was a big PITA: stuck between the bolt and end of CH. This is with a BCM bolt and pmags, so I didn't expect problems related to those.
I havent had the chance to get back to the range with my lovely bride and her (now) rifle to determine which round was being damaged. I did ask her and she can't remember. I may try to get to the range next week but if I don't then the next chance I'll get to go to the range will be in March (surgery coming up on the 5th that's gonna ground me for three months)
Almost always magazine related.
CarlosDJackal
10-20-08, 12:52
... Like I said, this only happened with the GA ammo, not the federal.
I missed the mention of GA ammo in the original post. A friend of mine also had issues with their ammo which leads me to think that this is probably the culprit. Have you tried these through a different rifle? Also, you might want to try and run a third brand through the same magazines (make sure that mark them before hand) to see if this happens again. If the third brand does not have an issue, then it is the GA arms ammo.
Good luck!!
P.S. Just because you can't shoot, it doesn't mean that you can't go to the range and watch you wife shoot, does it?
Heavy Metal
10-21-08, 22:03
Usually magazine related.
Sometimes overfunction related.
Sometimes buffer and spring related.
Sometimes tolerance stacking between the upper and lower.
The last three are rare and two and three are essentially the same thing.
Try a heavier buffer for shitz n' grins.
Friend,
Dump the GA arms ammo. I have posted this over and over warning people of the dangers of that stuff. I personally spend a good bit of time one day on a range in a remote area having my Father pick pieces of blown primer out of my face with tweezers from their "168 grain Match .308 ammo". Thank God I was wearing eyepro. The 5.56mm stuff gets even better as it has been the culprit of several Kabooms on AR15's. Do a search, I am sure something will come up. They use SAW (M249) brass for their remanufactured 5.56mm ammo dubbed Canned Heat. The chamber dimensions (headspace) on the SAW are somewhat different than what a 5.56mm AR is even more so than a .223 AR. What happens is the brass gets stretched somewhat during firing in the SAW. IMHO, their ammo is not safe. My incident happened in a bolt action rifle, and I almost never got the bolt free'd up from that incident. In the batch of 500 rounds I bought, I had more than 15 pop'd primers. I suspect that the brass from the .308 ammo was fired in the M240 as it was Lake City brass.
Link to M4 & M249 headspace info:
http://www.ar15barrels.com/data/headspace.pdf
9.95 times out of ten with two loaded rounds double feeding, it will be a mag related problem.
Keep an eye out on the training course announcements in this forum and the next time a man named Dean Caputo gets anywhere near your AO, drop the $250 on his class and go. It will be the best $250 you spend if AR's are your game, trust me. Two days with him will save you a lot of time in diagnosing malfunctions and knowing what it takes to make this weapon system run.
I had the same problem with hte ga ammo& i was using used orlite mags so i was'nt sure what the problem was i'm sure it's the ammo now.
Excellent thread! This is what I've experienced tonight while at the range. Everything that I was using, I bought NIB. Here's what I have:
Noveske n4lr (now=l-lrlp-556)------->>>http://noveskerifleworks.com/cgi-bin/imcart/display.cgi?item_id=r-lrlp-556&cat=47&page=1&search=&since=&status=
The add ons/swap (that required some disassembly to said rifle) that was done to it were MagPul's UBR and MIAD.
Ammunition was cheapo Remington 55 gr FMJ. In fact these same ones here still:
http://m4carbine.net/showthread.php?t=17506
Magazines used were MagPul's PMAG. Up till now, only a thousand rounds ran through said Recce. Rifle was and is clean[ed] before the shooting session. First go round, it shot fine. Second go round, first PMAG ran dry and changed out to number two (2) PMAG. "Bang-Bang"--then nothing! Did a quick turn to the side and saw two (2) rounds as is the discussion here. Kinda sorta close to what's illustrated by HES.
Dropped the PMAG, pulled the CH and locked the bolt back whereupon both catridges fell. Inserted PMAG till dry and topped off the session with my Glock 19.
As soon as I get home, I examine my n4lr to see what's up with what I experienced. Recce's clean, well lubed, but did notice something that was not there before. There appears to be a "gouge" of some sort in the chamber(?) with "white metal shavings"(?)(!) I did feel it and sure enough, it is a "gouge/scrape" of some sort on the top portion inside the chamber(?). Hope that it's no cause for panic! Any thoughts on that?I would take a picture, but don't have the digicam anymore.
Going to the range again tomorrow and "see" if it does the "double feed" again. Hopefully, maybe, it's nothing. But better for me to have found this out now than when. . .
Ok I'm mystified as to what can cause a double feed. My wife was having them towards the end of the day today. Here is the scenario
Colt 6920 (the bolt is not colt, but the carrier and everything else is)
Total shots fired: 146 rounds
Magazines: US GI 30 and 20 round types
Shooting positions used: Sitting, prone (both with 20 round magazines) standing (with 30 round magazines)(magazines were never used as a monopod)
Federal XM193...no problems all day
Georgia Arms 55gr FMJ - that's when the double feed problems occurred.
Now I have experienced the same problem when using GA in the past and am inferring that its the GA ammo. My question though is why? What would be wrong with the ammo that would be causing this.
Yes, many definitions on a double feed. A few tips for prevention: Change out your GI followers with MagPul anti-tilt followers. Buy MagPul magazines if you can get your hands on them. Make sure the magazine is being held in tight. Could be the mag or the mag release if it happens on diff. mags (magPul included)
FromMyColdDeadHand
12-23-08, 12:22
Please explain what you mean by double feed. If you mean 2 live rounds attempting to feed at the same time then it is magazine related. More than likely the magazine spring is worn. 20 rd mags aren't know for being the most reliable.
I always thought 20s were more reliable. No kink in the mag body. Now, most 20s will be older, so worn springs and feed lips may be more the norm.
Did anybody have him take a mag and smack the bottom to try to get rounds to eject?
I've seen alot of the newer AR's running the heavier extractor spring with the"Black" insert. The older lighter spring used the"Blue" insert.
I've also seen a variance in how hot ammo is loaded lately.
So what I'm thinking is your ar has the heavier spring and combing that with the lighter loaded ammo and there's the problem.
I run the lighter spring and don't find even my shorter ar's having extraction problems. I also find with the heavier spring the empty casing eject at 1-2 oclock from the gun which is discerning in my sight picture. Perferable is 5-6 oclock which makes for a nice neet pile to my right and behind me. But even a 3 oclock pattern is fine.
HelloLarry
04-28-22, 10:18
Apologies if dredging up old threads is frowned upon here.
Is a true double feed ever caused by under gassing?
What are the mechanics behind that?
Apologies if dredging up old threads is frowned upon here.
Is a true double feed ever caused by under gassing?
What are the mechanics behind that?
Double feeds CANNOT be caused by under gassing or over gassing. Double feeds are caused by bad magazines.
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