Blown primers on two new guns.

[blindhog1964]

I have an AR15 and an AR10 both new the AR10 is a DPMS LR260 the AR15 is a bushmaster. I finally got out to the range the last couple of weekends and decided to sight these new guns in. I was using factory ammo and since it was a sight in session I was using different types of ammo.
The AR 15 was first and shot right to point of aim with Winchester 5.56 then I switched to a Federal brand of ammo called Independence. Third shot gun locks up and will not eject. I did the pull the charging handle and tap the but on the bench and got it opened. I found the primer was blown and the case head looked swiped and flow into the ejector. Well enough of that ammo, on the third load and a blown primer, and pressure signs I thought that was all the testing I wanted to do with it. This ending the range day as it was late and the wife was ready for dinner.
So a week later I take the AR10 out for a spin. Same deal , sighting in. I had some Barnes and some Federal Premium. Got on paper and all was good no issues or so I thought. Picking up my brass found two rounds both federal blown primers again. So 2 different guns both new and blowing primers , but with only federal ammo.
I sent the 5.56 ammo back to federal and they say all checked with in spec. All I can say is I won be shooting factory ammo much anymore and when I do it won't be federal.

 

[243winxb]

Make sure the chambers are free of all oil & cleaning products. A wet chamber may increase bold thrust. Are primers pierced by the firing pin? Or blow on the rounded edge of the primer?

 

[blindhog1964]

They were gone only an empty pocket where the primer was. The chambers were dry. This happened after say ten to twelve rounds had been fired in each gun and only with Federal products all other ammo had no signs of pressure or blown or missing primers.

 

[G.barnes]

I think you just got a couple bad rounds. I shoot a lot of 5.56 almost all federal. Independance is not made by federal. It is made in Israel and imported by federal and is known to be a hotter load than regular xm193. I've not shot federal premium in 308 but I do shoot the federal NATO rounds. Never had a problem with them.

 

[wally]

Contact the ammo manufacturer or importer, perhaps a recall is in order, at the very least you should get the defective ammo replaced.

Primers shouldn't be blowing out and brass shouldn't be "flowing" into the extractor cutout!

 

[blindhog1964]

The Federal Premium loads are 260 Rem and yes I know that the independence ammo is made in Israel. I sent the independence ammo back to federal as per their request and revived a phone call that they checked out within spec. The 260 Rem ammo is still in my possession.
I agree about a couple of bad loads but in two different calibers and two different brands. I also have shot federal for years with no problems but I just can't seem to bring myself trust them much right now. I know the problem is probably no related to each other as they were produed I'm sure at different plants but it's just weird that the only ammo problems I'm having both have a common denominator and that being FEDERAL.

 

[blindhog1964]

Wally the flow I'm seeing is where the plunger ejector is resting on the case. The head stamp is almost completely gone and the primers missing. These are on both 5.56 in an AR15 and in 260rem out of a AR10. Both new guns.

 

[243winxb]

For both primers to fall out, pressure had to be very high or brass very soft. Maybe both? Firing 5.56 nato ammo in a 223 rem chamber may make problems as the nato is loaded hotter. The 260 Rem is a 60,000 PSI pressure cartridge. The 308 win at 62,000 PSI is higher. Strange. http://www.saami.org/specifications_and_information/specifications/Velocity_Pressure_CfR.pdf

 

[barnbwt]

223 is also a tighter chamber, and I imagine it could have a shorter leade (though I would think the wider breadth of weights out there for 223 would cause makers to leave it longer). Maybe a similar issue for the 308 if you are using a long or fat bullet profile that could be contacting the lands? Even if both were touching the lands a bit, it seems strange that pressure signs would be so gnarly (granted, 223 already operates pretty close to brass' limit). Did you try ejecting any unfired rounds to see if/how bad rifling marks on them were?

Both guns having similar issues can only be coincidence (unless you're shooting in 140 degree heat, or something) since you say you didn't load them, they're in different calibers (with different powders), and in very different (dimensionally) rifles. Most things that affect pressure are ammo related (powder, charge, bullet, crimp, etc.) and only a few things in the rifle that will do it (chamber neck dimensions, leade, bore diameter) and even fewer environmental (temperature). If the issue is just primers falling out, I seem to hear that one somewhat often among AR/223 guys, and I chock it up to a combination of cheap ammo (or primers) and a really high pressure round which allow them to loosen up sooner than other chamberings (308 not as much, though). Maybe sealed primers won't plop out as readily?

TCB

 

[MarshallDodge]

I have seen AR barrels marked 5.56 but they are still tight and cause the issue that you are seeing.

 

[blindhog1964]

The AR15 is stamped 5.56 I haven't made a cast for the chamber so I can't verify that it truley is. But assuming it wasn't I am still only having problems with the Federal ammo Winchester 5.56 shoots fine out of it and the cases show no abnormal signs of excess pressure. The same with the 260 rem Barnes ammo no problem no pressure signs. Federal ammo blown primers and signs of excessive pressure.
For right now I'm not shooting Federal in either gun until I can find a reason for this.

 

[Slamfire]

Make sure the chambers are free of all oil & cleaning products. A wet chamber may increase bold thrust.

This Army data shows, that any oily chamber does not increase chamber pressures, if anything, oil actually reduces chamber pressures. (might be lubricating the bullet and reducing the friction required to push the bullet out the barrel)




As for the increased bolt thrust, quality firearms are designed to carry the full thrust of the cartridge case, ignoring all friction between the case and chamber. Bolt thrust is only a concern if, the firearm was negligently designed to fail at less than maximum load, or was negligently built, and fails at less than maximum load. The second condition applies to the low number Springfield receivers, which is the actual origin for this canard. (1) An automotive analog would be, any manufacturer that designs and builds a ½ pickup truck (carries 1000 pounds in the bed) that breaks when you put 250 pounds in the bed, does not know how to design or build pickup trucks. However, if you fire 80,000 pound loads in your rifle, or put 1500-2000 pounds in the bed of your half ton pickup truck, even if it is well built, you can expect problems.

For right now I'm not shooting Federal in either gun until I can find a reason for this.

A prudent decision. It is likely that your rifles, being new, are tight. And that the Federal ammunition is at the top end of the pressure requirements, maybe even exceeds allowable pressures, but they shipped the stuff anyway. SAAMI specs allow something like a 12.8K psia difference in allowable pressures.

Unclenick wrote this on another forum:

The SAAMI system, when you look at it in detail, actually includes quite a bit of wiggle room for error. For example, a .308 Winchester maximum average pressure (MAP) is the average of the peak values for a 10 round sample taken when the ammunition is newly loaded. That average is allowed to go up to 66,000 psi for a 10 round sample pulled at any future time as the lot ages (maximum probable sample mean, or MPSM). The Maximum Extreme Variation (MEV) is the pressure a worst case individual round is allowed to reach, and for .308 Winchester the MEV is ±12,800 psi. So the maximum pressure for a new non-proof round will be:

62,000 psi + 12,800 psi = 74,800 psi.

That's not quite up to proof pressure (82,000-92,000 psi for .308 Win), but you can see how much wiggle room there is. In a .308 Win firing Varget under the 175 grain SMK, QuickLOAD says that would take a charge error about 5.8% too high to reach the upper side MEV, which is over 2 grains of powder. I know some handloader's powder measures are a little irregular with stick powders, but not that irregular.

Given the allowable top end pressure that SAAMI gives, and that there is no independent outside verification that Federal is even following SAAMI specs, I think the problem is the particular lots of Federal ammunition you have, not the rifle. And not oil either.

(1) Even before WW1, whenever the Army issues a defectively built weapon, or issues overpressure ammunition, and it blows up, the first thing the Army looks for is an oil can. If there is an oil can within 1000 miles of the defective weapon or ammunition, they blame the can. Sometimes they blame grease, sometimes the Army blames oil, but they never accept responsibility for the problems they created.