Lots of duds

Discussion in '223 / 5.56 MVP and Variants' started by DesertRatR, May 25, 2017.

  1. DesertRatR New Member

    Member Since:
    Oct 19, 2015
    Message Count:
    4
    I've got an MVP V&P 24" barrel chambered for 5.56. I've put about a thousand rounds thru it, a mixture of .223 and 5.56 with no complaints. The ammo was a mix of PMC and bulk American Eagle, all 55 gr FMJ. Then I got into my case of Winchester 5.56 55 gr FMJ. All of a sudden I started experiencing a lot of duds, maybe as much as 15% of the rounds wouldn't fire. I did try recycling them and none shot.

    I disassembled and cleaned the bolt. While I was at it I measured the firing pin extension at about 0.045 inch. Then went to the range to see how that worked. It didn't. I shot a box of the 5.56 and got 3 duds. Recycling them didn't shoot them. For comparison I had picked up a box of American Eagle .223 55 gr FMJ. Exactly 1 out of 10 fired. So I gave up.

    Mossberg told me there is a known problem with the thicker primers used in 5.56. Before I send the rifle to them I wanted to see if the community had any suggestions. But the number of .223 duds is really bothersome. I can't believe that the chamber has eroded to the point the rounds don't headspace properly. But could it?

    The photograph shows closeups of the two brand duds, the bottom the 5.56 and the upper the AE. The dimpling is noticeably deeper in the 5.56.

    Thanks for the help.

    Attached Files:

  2. boostless Active Member

    Member Since:
    May 5, 2014
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    201
    Headspace is set off the shoulder so I don't think your going to wear out the steel with brass. The top on looks like the primer may be seated a little deep but both look like they are light strikes. Manufacturers do use harder primers to help avoid a slam fire, which should be a null point since these rifles are designated in the NATO chamberings. If the firing pin protrusion is in spec it might be time for a new firing pin spring. I've heard of them wearing out through excessive dry firing sessions, so if you dry fire a lot this might be the case. If it were me I'd check the protrusion specs, then take the bolt apart and check the spring to make sure it's still in one piece(which you said you did), if it is send it back.
  3. spamassassin Well-Known Member

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    Aug 8, 2014
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    Your firing pin is short of what Brownells sets as minimim recommended by 5 thou. Could be wear induced. Yeah, after only a thousand rounds but keep reading. If it was just barely protruding enough to begin with say .050 it'd clear QC but, get some gritty dust on your primers a few times and whammo, you're .005 out of spec. Given the hard ass cups on 556 spec ammo, it wouldn't surprise me a bit. Send back, get nuther.
  4. DesertRatR New Member

    Member Since:
    Oct 19, 2015
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    Thanks for the replies. BTW, where on Brownells did you find the data? I couldn't find it. Also, I was looking to see if Brownells sells the pin, but again I couldn't find one. If I could buy a new pin I'd just replace it. The shipping is on the order of $35 (UPS ground), but Mossberg told me they are are close to 45 working days backlogged, so I figured I wouldn't see the rifle for 2 months. Replacing a firing pin is pretty easy.
  5. DesertRatR New Member

    Member Since:
    Oct 19, 2015
    Message Count:
    4
    Update to my previous post. I carefully measured the striker extension (fixtured the bolt, magnifier so I could see what I was doing, good lighting, etc) and got 0.051 to 0.052 after five measurements. A friend with the same rifle measure 0.052. So I am going with the striker as being OK. Also the comparison ammo I bought was American Eagle .223 marked AE223J. On some other forums I discovered folks who'd called Federal and were told this stuff has mil-spec primers. So perhaps they are the same thicker primers the 5.56 is using. Either way, the rifle has to be sent to the factory for spring replacement (that is what Mossberg told me they would be doing).
  6. Keith Moderator

    Member Since:
    Dec 7, 2014
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    Both my 5.56 and 7.62 have fired mil spec ammo without a problem.
  7. spamassassin Well-Known Member

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  8. BSJ Member

    Member Since:
    Jul 6, 2013
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    I started getting light primer hits and missfires, after I disassemble my bolt. I traced the problem to the tip of the firing pin slowly unscrewing itself from the rest of the firing pin assembly.

    A touch of blue loctite kept it secure thereafter...
    Keith likes this.
  9. GrocMax Active Member

    Member Since:
    Jun 12, 2014
    Message Count:
    167
    A firing pin protrusion of .050" is more than enough. What you are experiencing is more than likely a combination of circumstances- undersized ammo intended to fire in autoloading weapons (the curse of the black rifle market), hard/thick primer cups, and thinwalled soft annealed 23 degree shoulder cases. The primer strike will actually force the entire case forward without setting the primer off. Its not just 'headspace', headspace will more than likely check as being within SAAMI specs.

    Take a case fired in that chamber, do not resize, put a CCI 400, WSR or other thin/soft cup primer, fire it with primer only, note how ungodly deep the primer strike is. Now take a NEW case (mfg doesn't matter), sharpie the neck/shoulder area, put in a 450, BR4, 7 1/2 or Tula SRM primer and do the same thing, note how light the strike looks, or even experience a few FTF's out of 10. Look for the rub marks in the sharpie, note shoulder to neck junction.

    The difference between the measured headspace and the depth of the primer strike between the above two examples will be vastly different, its not just headspace.

    Setting the pin protrusion deeper won't help, might actually make things worse (more case head seps).

    Measure a new factory round base diameter, betcha its .373"-.374" right at the base. Look up the NATO style chamber- its .377"-.378" at the datum line .200" up from the bolt face. Measure a new factory round with a case length gauge, now measure a 223 go gauge- significantly under the go gauge length.

    What will help is getting the chamber cut to a tight SAAMI style and get rid of the loosey goosey crappy semi-auto NATO style. Leave the NATO chambers to black rifles. The ammo mfgs aren't going to start making ammo any different.
  10. Delavan New Member

    Member Since:
    Jul 11, 2017
    Message Count:
    11
    Sad thing is that the NATO chambering was, for me at least, a selling point. Now I'm reading about light primer strikes and breaking extractors...
    You reloaders know your stuff...to me, it was just the idea of a rifle that would shoot all 5.56mm/.223 you can get your hands on, without a hassle...
  11. wood chucker Moderator

    Member Since:
    Dec 19, 2012
    Message Count:
    1,627
    You'll be fine if you avoid steel case comblock ammo. I hate that stuff mostly because the bullets are copper washed steel jacketed inconsistent crap. I see no sense in pushing inaccurate steel bullets down a decent barrel.

    Mine run like champs and shoot better than I can hold them. Seriously my buddy mister F class smartypants shoots mine better than I can. I shoot brass cased hand loads ( mine only), Milsurp, commercial varmint and match ammo. No troubles to date.

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