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AR-15 Troubleshooting Tip's


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#1 1st cav sgt ret

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Posted 20 January 2007 - 04:41 PM

I'm borrowing this from AR15Armory it's very good useful information posted by Paul at BravoCompany
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Tech Info
This is some very basic information on troubleshooting and is not meant to be completely comprehensive, but it generally will address most of the common issued associated with the AR series of rifles.

This information assumes you have a working knowledge of an AR15 type rifle and practice safe firearms handling.

Short stroking (Failure to cycle)
Short stroking on an AR rifle is when the bolt carrier group does not cycle far enough to the rear to be able to strip a round from the magazine and chamber the next round. After firing a round, you will notice that the bolt is closed on an empty chamber, thereby forcing you to manually cycle the rifle to feed the next round. This occurs when there is an issue with the gas system.
To see if you have a short stroking problem and not a “Failure to Feed” problem, please perform this test first (assuming your bolt catch and magazine is functioning properly). Insert one round into a magazine that you know to be performing well. Insert the magazine into the magazine well, pull the charging handle to the rear, then release the charging to load the round into the chamber. Safely discharge that round. After the round has been fired the bolt should automatically be locked to the rear by the bolt catch and the empty magazine. If the bolt is closed on the empty chamber, then it did not travel far enough to the rear to be held by the bolt catch, and your rifle has short stroked.
Short stroking is a symptom of a problem with the gas system in the rifle. There are 7 parts of the AR gas system. In the upper receiver group, you have the barrel (gas port), front sight base, and gas tube. In the bolt carrier group you have the gas key, the carrier, the bolt, and the gas rings.

Assuming the rifle was running correctly previously (in the exact configuration it is currently) The following is a basic trouble-shooting checklist.
1) Ammo issue ? Commercial ammo does not run as hot as Milspec ammo, and some lots of commercial ammo may not be strong enough to cycle the weapon. Try a completely different type of ammo. If the weapon works correctly then you may have some bad ammo. This is becoming a more common problem with some of the low cost imported ammo, especially with milspec sized gas ports.
2) Lube and clean the rifle. Pull out your GI manual and properly clean the weapon. As a note, a little bit of dirt and carbon should not stop the proper cycling of your rifle.
3) Check the carrier (gas) key. If the carrier key is loose, the gas system will not hold enough pressure to fully cycle the weapon. Try a different carrier that you know to be working in another properly functioning weapon. If the weapon runs well with the other carrier, you may have an issue with your carrier key. The carrier key bolts should not be loose. It should be staked from the factory. Check to make sure the bolts securing the key did not rotate past the staking. The bolts should be torqued to 35-40 in/lbs.
4) Check the gas rings. (or just go ahead and change them – they are very inexpensive) Mythbuster: The gaps in the gas rings do not need to be staggered. I know we were all taught otherwise in recruit training, and yes I know it says they must be staggered in the GI manual. But this is a myth. As a note; it will not hurt the system to stagger the gaps in the rings, but if this single change makes the difference – you need new gas rings ASAP. Inspect the rings, make sure there are 3 of them, and that they are installed properly. Disassemble the carrier group, insert the bolt into the carrier, and hold the carrier vertically in the air. The bolt should not fall out of the carrier.
5) Change the gas tube.

Failure to Feed
A failure to feed initially looks similar to a short stroking problem. A round is fired, a spent case is extracted and ejected, but the bolt is closed on an empty chamber. The difference with a failure to feed is that the bolt did travel far enough to the rear to chamber a round. But it did not, and it is now closed on an empty chamber. Generally speaking, this is most often caused by a defective magazine (specifically a problem with the feed lips). You might also notice 2 dents in the casing that is still loaded in the magazine from bolt over-ride. The solution is to replace the magazine. USGI magazines are class 9 expendable and should be replaced when defective.

Failure to Extract
This is signified by a spent casing stuck in the chamber, not fully extracted from the chamber, or one spent casing and one live round being stuck in the chamber. (Sometimes one spent casing and one live round stuck in the chamber is called a “double feed”, but a double feed is technically 2 live rounds stuck in the chamber)
Assuming the weapon ran correctly before and is in the same configuration, this is generally an indication of a failure of the extractor. The extractor is made up of the extractor, the extractor spring, and the extractor insert.
First remove the extractor and inspect it for crack, chips or deformations. If it has any, then replace the extractor. The commercial market also has seen some MIM extractors, so if your extractor has any MIM/casting type markings then replace it. The most common wear point for the extractor is in the spring. As these spring wear out they become weak and do not have the proper tension to extract correctly. Replace the extractor spring and extractor rubber insert. Be careful to order the correct part specific to your weapon. There are stronger extractor springs on the market made to address the increased pressure that the carbine systems run under. These are recommended. Also the rubber insert you replace should be replaced with a black rubber insert. The original M16A2s had a blue insert. A stronger black insert was introduced for the cycling of the M4 and is an improvement over the blue and is good to go in both rifles and carbines. Another fix is the D-fender rings, or O-rings found on the market. Install them over your extractor spring. This was a standard upgrade for the M4A1s done by Crane Industries for SOCOM.
Now assuming you have these issues on a new built weapon, then you may need to go past the above advise and look at some other areas. Issues like this are most commonly involved on shorter barreled ARs. With a shorter barreled AR (generally 14.5”, 11.5”, 10.5”, 10.3”) you have about twice the pressure in the system with less dwell time (shorter than 14.5”) and a faster unlock time. One of the issues that needs to be addressed is slowing the cycle rate of these shorter barrels. This is done in part by the addition of a tungsten weight buffer. The M4 carbine runs a H-buffer and the M4A1 carbine runs an H2 buffers. There are also H3 buffers that see some use. Also stronger recoil springs will provide some aid. If all else fails you may need to look at gas port size and confirm that the chamber is not cut too tight.


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#2 1st cav sgt ret

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Posted 21 January 2007 - 11:24 AM

And another source that I reference a Lot is Armalite Tech note's

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#3 1st cav sgt ret

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Posted 24 March 2007 - 06:31 AM

Some really good information from Bushmaster
The Basic Drill
1. Unload the weapon. Remove the magazine and check the chamber, and then check the chamber again. With the bolt closed, pull the charging handle to the rear and release. Place safety selector on SAFE. Pull trigger. No matter what, that hammer should not fall. If it does, that weapon is not "mission capable". Furthermore, it is just as unsafe as possible, and by no means should it be loaded until it has been serviced by a qualified professional. 2. Place selector lever on FIRE. Pull trigger and hold to rear. The hammer should fall. While still holding trigger back, pull charging handle to the rear and release. Now release the trigger - you should hear a click as it moves forward. If no click is heard, the hammer is sticking on the disconnector and needs servicing. The hammer should not fall at this time. If it does, this is another very unsafe condition and should be checked by a qualified professional. Do not fire the weapon until it has been serviced. If you heard the trigger click as it moved forward, move on to: 3. Pull the trigger, the hammer should fall. If you don't hear the hammer fall at this time, it fell before and the weapon needs servicing. Or, the hammer is stuck on the disconnector and the weapon needs servicing. Either way, something is very WRONG - seek out a qualified gunsmith.

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Now is Not the Time to send a Message of Weakness,Now is the Time to Send a Message of Strength and Unity


#4 1st cav sgt ret

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Posted 24 March 2007 - 06:35 AM

Advanced Troubleshooting

At this time, we can go to the extended troubleshooting list. Remember, the steps of operation are;
1.Firing. 2. Unlocking. 3. Extracting. 4. Ejecting. 5. Feeding. 6. Locking. We'll take them one at a time:

1. FAILURE TO FIRE: The most probable reason for this is bad ammunition. Wait 30 seconds with the weapon pointed in a safe direction, remove the magazine, then pull the charging handle to eject the round, and examine the primer. If it has a good, deep primer strike, the ammunition is probably no good. If it has a light primer hit, it may be a hard primer, or the hammer spring may be defective or installed incorrectly, or there may be debris between the hammer and the forward wall of the lower receiver. A quick look in the lower will tell you. If it doesn't have any mark at all, the firing pin isn't reaching the round. The firing pin retaining pin may have been installed incorrectly (in front of the collar instead of behind it), the firing pin may be defective (short), or the hammer is not hitting the firing pin for some reason (not falling, hitting bolt carrier instead, debris in front, etc.). If, when trying to eject the unfired round, the charging handle is difficult to operate, the bolt may not have been locked fully forward due to an oversized round, or debris in the chamber. Riding the charging handle forward may also cause this problem. Remember, pull it back, and let go. NOTE: All AR-15 type rifles dimple the primer during feeding. This is completely normal for this type of weapon.

2. FAILURE TO UNLOCK: Very rarely does this occur, however, it's usual cause is either a bullet stuck in the barrel behind the gas port (a squib load) or the gas tube has been installed incorrectly. If your weapon did not unlock, CHECK THE BORE FOR OBSTRUCTIONS!! Do this BEFORE you fire another round. Remove the magazine, pull the charging handle to remove the spent case, let the bolt go forward, and push out the takedown pin. Open the receivers, remove the bolt carrier, and look down the barrel. If there is no obstruction, replace the bolt carrier, close the weapon, push in the pin, and take a look at the fired case. If the case looks normal, try another round. If the same thing happens, assume it is a defective part somewhere in the gas system (probably gas tube or gas key), and have the weapon checked out by a competent gunsmith.

3. FAILURE TO EXTRACT: This is a more common problem, usually shown by the fired case remaining in the chamber, while the carrier comes back to pick up another round, driving it into the fired case and stopping things up good. It is usually caused by a dirty chamber, a rough chamber, a weak extractor spring, a defective extractor, or bad ammo. A dirty chamber is self explanatory and only needs cleaning, while a rough chamber needs a careful polishing. Both can exhibit the same outward signs - light scratches on the fired cases, almost like a coating of frost. If the extractor is good it will usually rip a chunk out of the rim and you'll have to drive the fired case out with your cleaning rod. If the extractor is no good, then the rim will be intact - the spring is probably weak. A weak extractor spring is usually caused by overheating, another good reason to leave the bolt open after firing until the barrel can be held in your bare hand. This cools the bolt head at the same time, and keeps your extractor spring from cooking itself. The only cure is to replace the spring - a very inexpensive procedure. A bad extractor is a little more difficult to diagnose, but if you have already replaced the spring, replacing the extractor would be the next step. Bad ammo usually won't extract easily even if it is unfired, or the fired cases will show uncommon marks.

4. FAILURE TO EJECT: This looks much the same as failure to extract, except that the fired case is removed from the chamber. The bolt will either jam the fired case back into the locking lugs on the barrel extension (crushing it), or pick up a round from the magazine and try to stuff both of them into the chamber at the same time (looks like a double-feed, except one of the cases is fired). There are a few possibilities as to the cause of this problem, and one is the ejector. For whatever reason, the ejector is weak or sticking and just not clearing the round out of the receiver. A good cleaning might solve the problem, or it may require replacing parts. Try the cleaning first. The other is that the extractor is letting go prematurely. A new extractor spring will usually solve this right away. Lastly, the bolt carrier might not be traveling back far enough, but if it is in fact picking up a new round from the magazine, this isn't the problem. If it isn't picking up a new round, you probably have a gas leak somewhere. The best thing to do is to call us. We can go over it with you in detail, on a case by case basis. Our Customer Service number is 1-800-883-6229 (Mon- Fri, 8:30 AM - 6:00 PM EST).

5. FAILURE TO FEED: In our experience, 70% of feeding problems derive from bad magazines. Magazines have a service life just like any other part, and will wear out in time. For some reason, people never throw out their old magazines, even when they know they are no good. Some good signs of a bad mag. are: when the magazine starts to spread at the top when fully loaded; when it starts to double-feed 2 live rounds at a time into the receiver; when it fails to feed the last 2 rounds in the magazine. If you encounter any of these situations, trash that magazine. Another possible problem is an accumulation of dirt in the receiver extension, or buffer tube. Removing the buffer and spring and giving the inside of the tube a good cleaning will solve this problem. Failure to feed is not the same problem as failure to retain the magazine properly. This is either a bad magazine or a bad mag. catch. Replace the offending part. Cleaning the inside of your magazines from time to time isn't a bad idea, either. If a rifle has had no cycling problem before and develops a feed problem, the cause is usually a broken or loose Bolt Carrier Key screw. Check to see if screw are tight. If a screw is broken or loose, the key must be removed. The top of the carrier and bottom of the key must be cleaned before re-installing the screw and restaking them.

6. FAILURE TO LOCK: What usually happens here (assuming that the ammunition is not at fault) is that something prevents the bolt carrier from moving fully forward. AR-15 type rifles have a safety notch cut into the top of the hammer which engages the collar of the firing pin to prevent slam firing in the event of disconnector failure. A faulty "trigger job" can lead to this condition, as can an out of tolerance receiver, or a missing or stuck disconnector or disconnector spring. This condition will exhibit itself even when the weapon isn't being fired. Another problem that can cause much the same symptoms is a damaged gas key or gas tube. If the carrier cycles fine when not being fired, but jams when being fired, you can be pretty sure the problem is either in the bolt or the chamber. An ejector that protrudes beyond the front surface of the bolt will usually create an intermittent jam that can drive you nuts, and requires replacing the ejector. An extractor whose slot is not level with, or slightly below the bolt surface may cause the same problem. If the weapon has the same problem even when using a bolt of known reliability, then you can be sure that the problem is in the barrel somewhere. Remember that a failure to lock will also cause a failure to fire, so check things over carefully before ejecting the unfired round.

A SPECIAL NOTE: Lately we have been noticing that primers have been blowing out of their pockets at a much higher rate than usual. This seems to be a result of a diminished primer crimp applied to most .223 or 5.56 ammo by the manufacturer (probably to ease reloading). These loose primers can wreak havoc inside the receivers, causing all manner of binding, jams, and general mayhem. If you've got a jam that's driving you crazy, one that comes and goes, this might be the cause. A small rifle primer is just the right size to drop down inside the pistol grip screw hole and hide until the vibration of firing shakes it out, jamming the trigger but good. Compressed air will usually get these little suckers out, but sometimes you'll have to pull your hammer and trigger to get at it. It's something to watch for, anyway.

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#5 1st cav sgt ret

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Posted 21 July 2007 - 02:44 PM

Hopefully this'll work

Bushmaster operator's guide PDF

It is 3.88mb but you can download and print it it (Adobe)

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#6 GSH

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Posted 15 May 2010 - 03:54 PM

FAILURE TO FEED: In our experience, 70% of feeding problems derive from bad magazines. Magazines have a service life just like any other part, and will wear out in time. For some reason, people never throw out their old magazines, even when they know they are no good. Some good signs of a bad mag. are: when the magazine starts to spread at the top when fully loaded; when it starts to double-feed 2 live rounds at a time into the receiver; when it fails to feed the last 2 rounds in the magazine. If you encounter any of these situations, trash that magazine.

I found a solution for hanging onto old magazines...take them ouside and crush them with the sledgehammer. Then throwing them away....takes the temptation away...lol
An appeaser is one who feeds a crocodile, hoping it will eat him last.- Winston Churchill




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