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Thread: Critical Failure - Seeking Advice

  1. #51
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    You could try this: using a candle, soot up the bullet on one of the PP cartridges. Place in the chamber with your finger. Carefully tilt the barrel up (it should fall out) and try to catch it without disturbing any markings on the bullet.

    Can you see any engraving marks on the bullet from your lands? Compare to the photo below. Depending if you have engraving marks, and where they are, they might tell you if your chamber just might be .223 Rem (on the left) vice 5.56 (on the right).



    I know you stated (above) the Mossberg barrel is stamped "5.56 NATO" -- all this test would do is maybe verify it.

    - Mossberg OEM 16" M4 Profile 1x7 Melonite Barrel


    From AIM's site:

    New Mossberg OEM 16" .223/5.56x45 caliber barrels for AR type Rifles. These high quality M4 profile barrels feature a complete inside and out Melonite coating, 1:7 twist and M4 feed ramps.

    Specifications:
    -.223/5.56 Caliber [Edited to ask, "OK, which one is it?"]
    -M4 Profile
    -1:7 Twist Rate
    -1/2x28 Muzzle Thread
    -M4 Feed Ramps
    -Carbine length gas hole
    -.750" Gas shoulder

  2. #52
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    That's helpful - thank you!

  3. #53
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    This post will probably have WAY more information than you want but may help explain what you've been going through.

    My recommendation to you (and this is just a recommendation), now that you have checked for safe headspace, is to check what type of throat (SAAMI 223 or military 5.56) you have.

    Fire a single .223 Remington commercial cartridge and use a micrometer to find where, above the extractor groove, your case starts to swell (this will be the gap distance from the true face of the bolt to the rear of the supported portion of your barrel, starting at the chamber chamfer radius) and the distance to your bolt face.

    Use your micrometer and find the distance from your bolt face to the front of the bolt lugs (should be around .200 inches). This supports the case head.

    Subtract that distance from where the case starts to swell (where the chamfer radius begins) and you'll find the total distance where the brass cartridge case is not supported at all.

    Below is an exaggerated example of over pressure and cartridge case base expansion, you measure this with a set of vernier calipers or a micrometer. Also you will see brass start to flow into the ejector button on the bolt face and shows up as a circular ring on the base of the case. (easiest to see and the first sign of a pressure problem)

    US-made GI brass case walls are thickest here and is even thicker with Winchester and PMC brass. I don't know how PP makes their brass.

    Measure the dimension of that unsupported area (forward of .200 inches). Does it exceed drawing dimensions?

    Drawings below:




    Check how US GI brass is generally formed, and compare to where yours ruptured:





    Ned Christiansen post copied from M4carbine:

    Quote Originally Posted by Ned Christiansen View Post
    I've posted this before but I think it bears retelling.

    From a guy at ATK / Federal:

    "As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. Continued shooting of 5.56 ammunition in guns not chambered for 5.56 will show many warning signs of over-pressure, such as flattening of primers, smearing of the head stamp, dropped primers, blown primers and pre-mature wear on extractors and bolts.

    It needs to be mentioned, however, that several civilian manufacturers of AR15 type rifles have not adhered very tightly to the necessary chamber/throat dimensions of 5.56, while marking their barrels as “5.56 NATO”.

    It is my assumption that this is happening for two reasons: there is a belief that a rifle will shoot more accurately if the throat causes early engagement of the bullet to the rifling, although this is not necessarily proven.

    The other reason is likely that manufacturers, under extreme duress to supply large numbers of rifles, are not replacing reaming tools early enough.

    Because of this, some manufacturers’ rifles have a tendency to show signs of over pressure when shooting 5.56 ammunition, up to and including dropping and blown primers. This problem is easily remedied by judicious use of a finish reamer to provide that important amount of needed space, or to limit the rifle to a 223 diet."
    All done, if your chamber mics as a properly-reamed 5.56 chamber then you definitely have an ammo problem.

  4. #54
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    Every time I read one of sinisters posts I want to buy a hundred centurion rails.
    Why do the loudest do the least?

  5. #55
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    Because of Sinister's posts, I think this threadshouldbe a sticky. Excellent info!

    "Addressing the problem of shootings by ban or confiscation of non-criminal's guns is like addressing the problem of rape by chopping off the Johnson of everyone who DIDN't rape anyone while not only leaving the rapists' equipment intact, but giving them free viagra to boot." --Me

  6. #56
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    Okay, I took the carbine out tonight for a test run.

    I fired a couple mags worth of 5.56mm Winchester 64gr JSP and Winchester 62gr OTM. Everything ran like a top, zero issues. I inspected each piece of brass and saw no signs of pressure or anything to give me pause.

    I do not have any candles in my home, but used a marker an tried a 5.56 round as suggested by Sinister above. Slight marks appeared on the round 0.11" north of the case mouth. Visually, it looks to match the above pictures 5.56 round.

    At the risk of sounding stupid, I have a fired .223 Rem case, but I am unsure which dimension from the above drawing I am to compare it to. My engineering and print reading skills could use a freshen up.
    Please let me know, I will report back!

    Thanks again!

  7. #57
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    Where are the engraving marks compared to the orange line?



    Marks on the bullet of an unfired cartridge should start around 2.0026" with a 5.56 leade, 1.812" to 1.870" for SAAMI .223.

  8. #58
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    I believe they fall above the orange line. It's the max diameter of the bullet before it starts to taper - on a Winchester 62gr OTM.

  9. #59
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    I realize this is very subjective... I will try to upload a picture of it tonight.

  10. #60
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    This is the best I could get:


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