malfunctioning AR15

[ErikW]

My rifle more or less ceased functioning on my second stage of the 3 Gun Nationals. About every 2nd or 3rd round was a death jam and it turned a 40 second stage into a 159 second stage.

Here's the deal...

It's a 20" stainless DPMS barrrel on their low-profile upper, their gas block, their hard-chromed bolt and carrier. Assembled by my pistolsmith. Lubed with Slide Glide. I think the chamber is on the tight side, as it has been reluctant to manually unload a couple of my reloads. It's buffered by a standard A2 stock, with a slight amount of Slide Glide on the spring to prevent sproinging noises.

It has always run well, until a couple weeks ago when it would fail to eject the extracted round and fail to feed a round from the magazine. It turned out to be horribly dirty, and cleaning it cured it. It ran for about 80 rounds in a three gun match before cleaning and lubing it before the nationals.

It ran fine the first stage, about 30 rounds of moly-coated Sierra 69 MatchKings over Win 748 in once-fired LC99 cases (2750 fps). On the next stage it ran for about 10 rounds before the problems began. Firing prone from a 30 round GI magazine, it was failing to eject extracted cases and failing to feed rounds. It might have been trying to feed both the fired case and the new round. At least one round fed into the extension and set back the bullet. At least one fired case was stuck between the bolt and the receiver. At least one fired case failed to extract from the chamber. Hand-cycling the action wouldn't clear the jams. Dropping the mag and cycling wouldn't clear them. Changing magazines didn't cure the problems. Firing with the mag off the surface didn't cure the problems. I had to go in and remove cases and round by hand. One even required me to use a loaded round to pry out the case, I think it was the one stuck between bolt and receiver.

It was not at all dirty. I cleaned up the bolt, carrier, and extension lugs and applied Kellube instead of Slide Glide. On the function fire range it ran for maybe 20 rounds before malfunctioning in much the same manner. I spent ten minutes with my knife prying out a case that had stuck between the bolt and the charging handle.

I took it apart that night. Extractor hook looked good, and I could barely move it by hand. The ejector required a tool to push down and it didn't hang up. The carrier mated with the gas tube just fine. There was some gas blow-by around the front of the gas block, which I recall is normal, though maybe there is a little more than usual. The block wasn't loose.

What could be the trouble?

[Les Snyder]

Eric... ....FYI...dont know if this will help, but I had about 3000 rounds thru a 16inch A3 flat top, when cleaning the bolt with a toothbrush, rolled one of the gas rings off.  The ring was worn almost 1/2 the thickness on one side.  I have a friend that worked on the M4 project for SOCOM and he gave me an extractor upgrade kit containing a one piece ring (like the McFarland ring) a neoprene "O" ring that fit around the extractor spring/insert under the rear of the extractor to aid stiffness, and a new alloy ejector spring.  The one piece ring is pretty slick, and Mike commented that the ring should last the life of the barrel...your problem sounds like extractor problems to me... regards Les

[TMC]

Gremlins, bad karma, or maybe your competition put a voodoo curse on it.

Did you check to see if the gas tube and gas block ports are clear?

I still think its an extractor problem.  I tried everything else with mine before replacing less than $5.00 worth of parts that did cure it.  Go with the cheap fix first.

Good luck!

[Old and Slow]

Erik, saw you at the function fire range as I was pulling out but thought you were sighting in. Since you mentioned that there seemed to be a little more than usual gas blow-by around the carrier key, we use to run solvent soaked pipe cleaners (used to clean the smoking pipes of old) through the carrier key. The caked-on crud would accumulate in that portion, thereby reducing the amount of gas used to move the bolt carrier rearward. I think the old Nam-era M16 cleaning manuals even suggested using worn out bore brushes to the clean the carrier key.

Did you happen to check out the three bolt rings? With the bolt assembly in the bolt carrier (without the cam pin), you should check for binding as you move the bolt back and forth. Also, the bolt shouldn't drop out of the carrier if you turn the assembly to point downwards. Stagger the bolt ring gaps to prevent loss of gas pressure.

Double check your action spring. The free length should be 11 3/4 inches minimum and 13 1/2 inches maximum.

I also remember having lots of stubborn caked carbon on the tail end of the bolt, behind the rings. I use to scrape this area with a dull knife blade to get it clean.

Hope one of these is your solution.

[Shooter Grrl]

Tom?!?  Is that you???

[Carlos]

Carbon build up deep in the carrier hole (behind the bolt) is easy to miss and <could> cause malfunctions as you describe. They make a special cleaning tool for this area but I made my own out of a 4-in-1 screwdriver. Check the area with a flashlight - if there is carbon there, soak it in carbon solvent and later use some sort of long scraper to get it all out, you want to be careful to to scratch through the "flash crome" plating in the hole in front of the carrier - its quite thin. A brass scraping tool works well.

The M4 extractor upgrade kit might also help - though these are expensive. Anyone know who has a good price on these? They look like about 50 cents worth of parts.

[David Benzick]

I just purchased a heavy duty extractor spring from Specialized Armament Warehouse for $5.  

My rifle choked just about the same time as Erik's and with similar symptoms.  I cleaned heck out of the chamber on the advise of Benny Hll, who I had the pleasure of squadding with at 3gun Nat's.  The rifle ran great at the function fire range for thirty rounds and then choked on the Gully Whacker stage 8 times.  Ouch!

I then wrapped some 000 steel wool around the old chamber brush and cleaned HELL out of the chamber on the advise of Bennie Coolie.  I didn't test fire the rifle and it ran great on stage 2.  

Tonight I plan on doing some serious blasting with that rifle to see if the heavy duty chamber cleaning solved the problem.

Theory:  Post cleaning carbon residue in the chamber attracts additional carbon which builds to the point where extraction becomes difficult.  Difficult extraction deforms the soft brass rim on my Federal cases and as the case mouth clears the chamber the case is tipped to starbord by the ejector just enough that the extractor loses its purchase on the deformed case rim, leaving the empty just to the rear of the chamber.  The new round then stuffs underneath the old case.  Insert profanity here

I will get back to you on the results.

[sfinney]

I have heard from a reliable rifle builder that the DPMS rifles are very tight, all over - they are max spec evidently. Including tight chambers. My DPMS bull barrel almost wouldn't mate with my DPMS bolt carrier. It was a very snug lock up. It eventually loosened up, but I exerienced some similar malfunctions before it finally broke in. You might want to have someone check your headspace, and also chamber dimensions - it might be worth "loosening" it up some.  

A properly broke in stock rifle should be able to go several hundred rounds withour requiring any cleaning.

I once saw an OVER lubricated rifle experience some wierd problems - it had to much heavy lube applied to the bolt carrier, as it cycled the lube slopped forward into the chamber. The high temps baked it on in almost a varnish form in the chamber, causing the bullets to almost freeze in the chamber, and not extract properly.

A few points: Don't over lubricate an AR, and use lube thats known to work in AR type rifles. Break Free with CLP was engineered specifically for AR-15/M-16 rifles once upon a time, and works well.

Most excessive wear in ARs comes from overheating.

Other malfunctions usually come form "tuning" the rifle out of stock condition (trying to speed up or lighten the cycling, etc).

Just food for thought.

(don't get me wrong, I use Slide Glide on my pistols, its wondeful stuff - but if you read Brian's directions, he advises using it on stock guns, and LOOSE open guns. If you're tolerances are really tight in your AR, a different lube might be in order. or not.)

(Edited by shooter40 at 7:28 am on May 11, 2002)

(Edited by shooter40 at 7:33 am on May 11, 2002)

[sfinney]

Off of the Bushmaster website, trouble shooting section:good info. (By the way, I highly reccomend Bushmaster rifles, especially the V-match models!)

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, exept 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, exept 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 reciever. 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.

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.

[ErikW]

So, with a new extractor spring/insert and a D-ring I've never used before, I took the clean gun to the range. Functioned flawlessly for maybe 75 rounds of my 55gr W748 loads. When I ran out of those I put in my 55gr 2200 loads (faster powder, less gas?). It malfunctioned right away. This time it was ejecting the spent brass but failing to feed. It shoved rounds below the extension, such that the crimped bullets were set back in their cases and spilled powder. WTF?

[THS]

Erik,

First let's eliminate one thing.  Buy, yes I know that hurts, some good 55gr factory ammo and test fire a clean weapon.

I have extensive experience with national match M16's, and the problems you describe could be several things.

Eliminate your relaods first.  Don't use Federal 69gr GM for this; I have seen and shot many AR's that would not extract that ammo.  Take a minimum chamber and pressures right at SAAMI spec, and you'll get poor extraction with the smallest bit of crud in the chamber or temp spike.  Fed GM is great ammo, but some guns don't extract it well.

I don't have a lot of experience with your powder choices, except to say that VERY few NRA HP shooters use ball powder due to temp sensitivity.  3 Gunners tend to pick spherical powders so they can keep the dillon going, but there is a trade.

I don't mean to insult your reloading skill; please don't be offended!

Tom

[Carlos]

Agree, I have a National Match upper custom built and custom throated by White Oak precision for reloads using bullets up to 80 grains; many of my national match 600 yard reloads will easily choke the other AR uppers I have (Colt M-4, Oly bull 20", no-name 11.5" w/ 5.5" flash hider).

Unfortunately for us 3gunners who are forever doomed to tinker with our guns and loads, off the shelf ARs are made to shoot 55 and 62 grain factory ammo. In the design, they are "timed" to function with standard factory ammo out of 20" barrels (one reason the shorter guns often have problems leading to some bizzare solutions like the corkscrew gas tube).

As was discovered early on with the first M-16s, deviations from factory loads, or reloads duplicating factory, can be disasterous.  Please let us know how testing goes. Regards, D.

[jhgtyre]

I am also a slave to my Bullet Drop Compensator.  It is setup for factory 55gr so no heavy bullets for those long range shots for me.

[ErikW]

Update: ran about 15 rounds of Win Q3131, about 35 rounds of reloads with 4895, and about 30 rounds of various reloads with W748, including the load that failed at Las Vegas. Not even the slightest hiccup.

Could it be the 95+ F temperature of Vegas cooked up the sensitive W748 so much it caused my trouble? I would expect blown primers or something like that, not what I experienced.

[David Benzick]

I had similar extraction problems at about the same time as Erik and solved it with a heavy duty extractor spring from Specialized Armaments in AZ.  The rifle runs great now.

[danny]

moly coated reloads in a AR , has  anybody else used um. had any problems .