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Thread: Blown Primers with AE .223

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    Blown Primers with AE .223

    Let me first start off by saying, yes these two incidents happened in two different Bushmaster brand M4's each of which I can say have 5.56mm chambers. The ammo in question is Federal AE .223 55gr. FMJ BT. It is a relatively recent lot, as the color used in the sealant seems to have changed from the red that I have seen in every round previously to a new blue colored sealant.

    Let me describe each failure.

    Incident #1 took place in carbine A (I could describe the carbine, but only if asked) It consisted of a round that failed to eject, it was wedged inside the upper between the bolt face and the back of charging handle, resting in the charging handle channel. Also against the bolt face was a round in the process of being stripped off the mag, but couldn't because the bolt's movement was mentioned by the aforementioned case. When popped out, the empty case had three distinct features. First and most obviously, the primer was missing, a scorch of blackened soot left in its pocket. Second, the case had a "belted" effect. Finally, the case showed very strong extractor claw markings, digging into the brass.

    Incident #2 took place in another carbine, carbine B (Once again, if you feel it is necessary I can describe them both) This incident was much more mild. The empty case had simply created a sort of horizontal "stove pipe" where the top of the empty case was wedged against the front of the ejection port. This case showed no sign of belting, but again, the primer was blown out, not to mention the heavy extractor claw marks. Also, but I attribute this mainly to the stovepiping, the case head was crunched severely.

    What is wrong with this? You have nearly identical issues happening in two different carbines, with the same brand and lot of ammo, at this point, I'm going to call it ammo and shoot the rest of this batch up. What do you'all think?

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    How are you sure they are 556 chambers? Have they been checked? Don't just believe the manufacturers statements or markings.

    The only time I've seen or experienced blown primers is in a non 556 spec chamber. It sounds like both carbines would benefit from a 556 chamber reaming.

    This is a classic problem................
    Last edited by carshooter; 08-01-07 at 01:07. Reason: More information

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    Quote Originally Posted by carshooter View Post
    How are you sure they are 556 chambers? Have they been checked? Don't just believe the manufacturers statements or markings.

    The only time I've seen or experienced blown primers is in a non 556 spec chamber. It sounds like both carbines would benefit from a 556 chamber reaming.

    This is a classic problem................
    Both carbines have been headspaced for 5.56. I would think this means they are 5.56, right? If headspacing can't fully ensure that they are in-spec, where can I have a chamber reaming done? I assume it will destroy the chrome lining?

    Also, this is the first time they have had any blown primer issues at all. I've fired over one thousand rounds of Guat 5.56, at least one thousand in Winchester in both .223 and 5.56, not to mention close to one thousand of AE .223 previously. So this means, carbines with nearly four thousand rounds between them start blowing primers in the same batch of ammo? It simply seems to me the culprit is the ammo. I don't mean to be blocking out your explanation, I just think that this info leans heavily towards the ammo, but if I knew the answer I wouldn't be asking for help.

    Still, if the culprit is the carbines, are there any other problems besides the chamber that may be causing this?

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    The blown primer, expanded case head and extractor pull marks on the first example are all in-line with an over-pressure cartridge.

    I'll call it ammo as well.

    Now, as for chamber dimensions, you have much to learn.

    The minimum chamber length for 223 and 5.56 are basically the same.
    It's the diameters and maximum lengths that are different.
    Headspace gauges check the LENGTH of the chamber.
    It's much more difficult to determine the DIAMETERS of the chamber.
    The established method is to fill the chamber with a casting alloy, pop it out, wait a prescribed time for it to cool, then measure it.

    Here is some light reading:

    First, look at my collection of headspace gauge dimensions.
    Note the similarity in length of the "go" gauges as those are the "minimum length" specs for a chamber.
    Minimum length determines the ability for a chamber to fit a cartridge that's made to proper specs.

    Then look at my 223 and 5.56 reamer dimensions collection.
    Note the body diameters at the shoulder and at the base.
    Those are the two that have the most effect on reliabaility AFTER the headspace length.

    Lastly, read through my how it works thread and pay particular attention to the over-gassed symptoms as these also show up on over-pressure ammo that causes the gas system to have more pressure than normal ammo would.
    Randall Rausch
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    I don't think you have a chamber problem (usually a popped primer problem is 5.56 NATO shot in .223 chambers). The marks on your brass are likely because the extractor is scratching it while it slips off. If you you're not using an H buffer I'd suggest getting one. AE223 is commercial ammo, sometimes primers will come out of them pretty easily as they aren't crimped like military ammo is.

    To me it sounds like an extraction problem. I think your extractor is letting go too soon (extractor being overpowered by the ejector). The extractor pressure has to be strong enough to hang onto the empty casing long enough for clear ejection as the bolt is traveling rearward. If it's not strong enough it'll let go too soon before the casing can clear the ejection port and then this empty casing gets jammed up in the upper receiver with the next live round thats fed from the magazine as the bolt moves forward.
    'Back in the day' a fix was to trim the ejector spring a little (not okay on full autos). This was before stronger extractor springs, black buffers and Crane O-rings were available. I would suggest against doing this.


    To fix your problem I would do the following:
    Give the ARs a really good cleaning, clean the chamber really well. Clean the bolt, remove the extractor and clean it really well. Lube the ejector and lube up everything well. While you have the extractor off of the bolt rub your finger underside edges of the extractor hook you should be able to feel the distinct edges of both sides of it (it should have peaks on each side of it). I you can't really feel them much, replace the extractor, pin and extractor spring w/buffer. If these need replacing I'd suggest buying the Bravo Company SOPMOD BCM bolt upgrade kit. It consists of a new extractor, extractor pin, upgraded extractor spring, black buffer and Crane O-ring. They sell for $30 and are a good upgrade for any AR.





    I would suggest using this SOPMOD BCM kit (along with the stuff below) to anyone getting their equipment (and self) ready for taking a class. You don't want to be 'that guy'.

    For class I would suggest to replace these parts on your AR or have them with you if yours is already GTG:
    1-new SOPMOD BCM bolt upgrade it.
    1-new buffer spring
    1-new gas tube and roll pin
    1-new cam pin
    1-new carrier key and screws (better yet an entire GTG complete bolt and carrier group)
    1-new hammer, trigger, disconnector and related springs (if your running a match trigger groups use these for when yours fails)
    5-new magazines
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

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    In an effort to help quickly, I dashed off my reply at 1:00am after a long day.

    I ignored that the ammo in question was AE 223 and replied giving my Q3131A or XM ammunition experiences.

    The extractor upgrade suggestion is exactly what I'd try first.

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    Thanks guys, I'll buy the BCM parts kit. One thing though, I clean the chamber, extractor, and bolt face very well, every time I clean my AR. Also, when this happened, I had added an O-ring to my extractor spring. If this info helps narrow the problem down then I hope to have no more of these failures when I crack open the next case of AE. Gotm4, I'll buy the BCM kit for now, and before I take a class, I'll definitely buy each of the items you listed (Well, probably more than 5 mags )

    AR15barrels, thanks for hooking me up with some good info, I guess I really don't know as much as I should.

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    Quote Originally Posted by BushmasterFanBoy View Post
    Thanks guys, I'll buy the BCM parts kit. One thing though, I clean the chamber, extractor, and bolt face very well, every time I clean my AR. Also, when this happened, I had added an O-ring to my extractor spring. If this info helps narrow the problem down then I hope to have no more of these failures when I crack open the next case of AE. Gotm4, I'll buy the BCM kit for now, and before I take a class, I'll definitely buy each of the items you listed (Well, probably more than 5 mags )

    AR15barrels, thanks for hooking me up with some good info, I guess I really don't know as much as I should.

    Let me know if it takes care of the problem. If you had the O-ring on there then it's probably a bad extractor.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

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    Quote Originally Posted by gotm4 View Post
    If you had the O-ring on there then it's probably a bad extractor.
    Or one particularly hot round...
    If the rest of the case is working fine and you have just a single problem, it's most likely the ammo.

    If you have continous problems in an otherwise good gun, then parts (extractors and springs) are wearing out as suggested above.

    Are all the other cases from this batch of ammo showing strong extractor pull-marks on the brass?
    If so, get a heavier buffer for sure.
    It's better to delay the extraction with a heavier buffer than just to strengthen the extractor so it can prematurely yank the case out of the chamber.

    The best solution is to just upgrade everything.
    That way the extraction timing will be correct AND you will have a stronger extraction system.
    Now, when you DO get a hot round, the gun will keep on ticking like a Timex...
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

  10. #10
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    Do you have lot number or numbers from the ammo? Was it in LC or FC stamped cases?

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