A lot of duds with Winchester 5.56

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DesertRatR

New member
I have a Mossberg MVP V&P in 5.56 (24" barrel 1:9 twist). I am shooting Winchester 5.56 mm 55 gr FMJ ammo. This is out of a 1000 round case I bought several years ago.

I am getting quite a few duds (1 out of 20 is typical with 5 out of 20 in one box). The primer dents on both fired and dud rounds look about the same to me. And they look a bit on the light side. I have shot .223 (mainly American Eagle and PMC). I don't think I had anywhere near as many duds with the .223, if any.

I am trying to figure out if I have an ammo problem or a gun problem. I have read a lot of articles on 5.56 vs .223, including the June 2012 Lucky Gunner Labs article with his test data. But I am not sure I learned much to help me figure this one out.

I can find exactly nothing about the primers used in the Winchester ammo. So I don't know if I have hard primers, or what.

I gave 5 of the duds to a friend with the same rifle, to shoot and see if they fire in his gun or not, when he gets around to it. In the mean time, if anyone has any ideas, thanks for the feedback.
 
have you tried feeding the ammo through a second time. I've had some hard primer ammo in handguns where they would eventually go off if you reloaded them enough times.
 
If the ammo is clean and fires reliably in other rifles of the same type, it's probably a rifle problem.

Check the chamber to assure there's no crud or rust.

Clean the firing pin/bolt. Check rifle headspace and firing pin protrusion from the boltface.

Replace the mainspring as a last resort.
 
If you don't want to dis-assemble the bolt, hose it out well with Brake Parts Cleaner, blow clean/dry with compressed air, and re-lube with your choice of thin lube. See if this helps.
Otherwise, try a different brand/type of ammo.
 
Could be a weak hammer spring. I get light strikes with some mil spec ammo or when I use CCI 41 primers in one of my ARs that has a Timney trigger install. It does it about the same frequency described. I upgrade the spring and it still does it.
 
It's is no comparison but . . .

Well, I understand that IT IS REALLY NOT A GOOD COMPARISON, but lately I've experienced a lot of Winchester duds in 22LR, and the one time I shot Winchester 45 colt the bullets were not crimped well and would creep forward in response to recoil far enough to prevent the cylinder from turning.

Life is goods.
Prof Young
 
Mossberg acknowledged this as a known problem with 5.56. But before i send them the rifle I'll try to fix this myself. I'll disassemble the bolt and clean it good. Where is a good source for a slightly stiffer spring?
 
Could be a weak hammer spring. I get light strikes with some mil spec ammo or when I use CCI 41 primers in one of my ARs that has a Timney trigger install. It does it about the same frequency described. I upgrade the spring and it still does it.
Click to expand...
Im just spit balling here.. have you checked the firing pin?
Im wondering if it has not bent or is maybe out of spec? if it's not protruding enough no amount of hammer behind it will get the job done.
 
I disassembled the bolt, but not the head. Things weren't very dirty. I cleaned everything with some gun cleaning solvent, dried, very lightly lubed, mainly wiped it down with an oily patch (I use Break Free CLP) and reassembled. I measured the firing pin extension and got 0.045 to 0.046 inch. Somewhere I saw someone who thought it should be 0.035 to 0.045 inch, but I can't confirm. Assuming that number is about right then the pin extension is OK.

I don't recall having this problem with some Federal .223 I shot up a while ago. Today I got a box of Federal .223 and will be off to the range in the morning, along with a box of my 5.56. If the problem persists with the 5.56, but not the .223 then I'll send the rifle to Mossberg.
 
Sounds like a sloppy chamber / bad head space; or bad ammo.

Shoot some PPU ammo in the rifle, and see if it does the same thing. (They use "NATO"-spec primers which should be a worst-case scenario; and it's not very expensive.)

If the problem remains, it's a bad chamber or bad head space.
If the problem does not return, I'd say it's bad ammo. (Under minimum dimensions -- something common for Remington, but not Winchester or PPU.)
 
Its not the ammo.

Odds are its the head space is too loose.

Possible firing pin issue, I would say 80% head space.

OP says one type of ammo and the thinks not others but states id did occur with others as well, he just did not count them.
 
duds

I doubt it's the ammo. MOdern factory ammo is pretty darn reliable, and has to be really mistreated to yield the poor results you are describing. Especially if you are getting some fail to fires with other ammo, as you admit you might.

I am most curious about Mossberg admitting some type of issue "with 5.56mm". What exactly have they admitted to, and in what fashion?
 
Here is the email I received from Mossberg Customer Service: "We have seen that the bulk 5.56 ammunition have thicker primers which can cause similar light primer strikes. Our service department has determined a way to correct this from happening, but we would need to get the whole rifle into our service department."

After I pestered them a bit more about exactly what the problem was (and if they would sell me the spring and striker-should be cheaper than UPS ground), I received this: "So I did follow up with the service department regarding this issue with the MVP 5.56 light primer strikes. The springs in the striker assembly and trigger assembly that need to be replaced are installed with a special fixture that we use in the assembly line, so the service department would need to get this in to correct the issue."

I don't see why the trigger spring effects it; perhaps that is just pre-emptive. BTW, I've gone back and carefully measured the extension of the firing pin and got 0.051 to 0.052 inch (five measurements). A friend has the same rifle and he measured 0.052 inch for his pin extension. So I am going with the weak spring. I thought around shimming it, but I have no ability to really measure the spring stiffness, nor do I really know what stiffness should work. And after looking over the Tacti-Cool.com website on this subject it is probably better to let the factory fix it. It would be cut-and-try for me (and maybe wreck something). So the rifle is off to TX for service.
 
Light primer strikes are also a symptom of too much head space.

Case never touches the shoulder, firing pin hits it, it moves forward.

I have seen good dents that did not fire as it was giving when it hit and it finished denting when it did come to rest but the require sudden impact do touch it off was gone.

The fixture needed is a receiver fixture and head bolt adjustment.

Spring needs a fixture to put in place, not in any system I have ever seen.

If it comes back fixed that's fine, I would have done a head space check before sending it off and see what it is when it comes back.
 
Keep us updated on this.. IM really curious to find out if it's a headspace problem like many are thinking, I'd be somewhat shocked and appalled if that was the case.
 
Rifle is going off next week. I have no way to check headspace. And I'll suggest it in the note I leave in the box. I'd be surprised if that was the problem. Until recently the rifle worked flawlessly. It is only the last few boxes of Win 5.56 that are problematic.

Stay tuned.
 
Ahhh, more information trickles in.

Then yes it points to a firing pin issue.

Having had more than one AR apart, it does not take anything special.

I put triggers in a couple.

Sounds like Mosburg CYA but if they fix it that solves that.

Better yet, get a Chrome Two State Trigger from Rock River Arms.

Now that is a nice AR trigger, Match graded but still has the two stage pull.
 
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