Split necks in 223 cases issue

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Sommerled

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I recently bought a new Sig 556 rifle and finally got to shoot it this weekend. To break it in I used 50 rds of new factory LC 55gr Nato loads that I bought three years ago. I like the rifle and had heard it was hard on brass but.. when I picked up the brass to bring home to reload, 42 cases had split necks and are unusable.:cuss:. So I fired 10 handloads with new Lapua brass and three of those cases had split necks too. (load was 69gr smk and 23.4gr of H335).
I am wondering if I got a rifle with a defective chamber? None of my other rifles do this unless I've reloaded the brass too much and the necks got hard.

Should I return this rifle? I don't want a brass "terminator". Maybe there is a fix?
 
Measure your "fireformed" (split) cases versus the unfired cases.

For all of our curiosities' sakes please post up what you find, but if you find a significant expansion in the fired neck OD, shoulder, etc, I'd be real worried about that chamber and consult with the manufacturer.

One type of brass/ammo I'd say bad batch, but with two, that's unacceptable whether a rifle has a "rep" as hard on brass or not. Something has to be up.

Not sure whether you're either....
...the unluckiest guy I've heard of with two unrelated bad batches of ammo.
...oversized chamber - have an enfield I call the "splitter" due to shoulder/neck slop so been there.
........as yet unknown, let the best of us not leave out the "simple and right under your nose" item possibility just in case :D
 
I'd be on the phone first thing Monday morning - but I might not volunteer immediately that I was handloading.

One batch of bad brass I could see happening - unlikely, but possible. Two? Not unless you are the unluckiest guy in the world. But to have two bad batches, with one of them being Lapua? No way, IMO.
 
Tim the student-

One of the batches of ammo was NEW Nato.

I am on the side of the chamber being suspect although this should have showed up at test firing if the operator bothered to check the fired case(s).
 
I was just given about 500 rounds of LC 5.56 Nato brass that was fired by the local PD, and about 10% had split necks. These were all factory rounds, of recent manufacture, and fired in the department's M16's. This was green tip ammunition, since there were a couple of unfired rounds in the mix.

Rather than mess with them, they all went into the scrap bucket.

Hope this helps.

Fred
 
He pointed it out because it was factory fresh ammunition, not reloads.
Click to expand...

I assumed they were fresh from the factory, not reloads. Factories will still get a bad batch too. He also said that:

I fired 10 handloads with new Lapua brass and three of those cases had split necks too. (load was 69gr smk and 23.4gr of H335).
Click to expand...

So, I'm still confused about why he pointed that out.
 
The neck diameter of cases fired in the Sig 556 rifle is .257 in. in both the factory NATO rounds and the Lapua handloads. the cases were stretched .004 from the shoulder back according to my wilson case gage.
Diameter of cases fired in my RRA AR is .254. Those fired in my Savage bolt gun are .255.
This doesn't seem like much of a difference.
Reloader fred's input that he found split cases in once fired cases he obtained is interesting. But haven't we all been using once fired military cases for a while? Maybe the recent supply of nato surplus ammo is there for a reason?

Like Tim said, I'll be on the phone tomorrow! It appears to be a loose chamber?
 
But you also split Lapua necks. Lapua makes the best brass on the market and all the necks are annealed. Maybe the round is catching on something as it feeds, causing the neck to get sliced and weakening it catastrophically.
 
No scratch marks. The vertical splits are random. Some have one large,easily seen one, and others have several around the case neck. The Lapua case splits were harder to see and were very fine striations that you could just see light through using a magnifier. I will not use the other seven cases again though. expensive waste.

I am looking at the Nato brass again and just noticed that most of the splits, when there are two, are directly opposite each other!?

If I get a hold of Sig Arms tomorrow I'll post what they say.
 
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Just for information, I just checked all the brass I put in my scrap bucket from the stuff I got from the PD. It's all headstamped LC 08, so it's fairly recent manufacture.

Hope this helps.

Fred
 
Not good, not good at all. There is something seriously out of spec with that chamber, headspace or something. I wouldn't feel comfortable firing even one more round out of that rig, it is seriously flawed my friend.
 
The neck diameter of cases fired in the Sig 556 rifle is .257 in. in both the factory NATO rounds and the Lapua handloads.
Click to expand...
Drawings for the 223 chamber showes a maximum of .255" + .002" With spring back of the brass, i would say you have an oversize neck. amlevin>
Tim the student-

One of the batches of ammo was NEW Nato.

I am on the side of the chamber being suspect although this should have showed up at test firing if the operator bothered to check the fired case(s).
Click to expand...
"the operator" meaning the factory person that test fired the rifle before leaving the factory. New owner & Siq, both test fired with factory ammo. When Sig test fired, they should have seen a chamber problem if there is one. Take note, Nato ammo not to be fired in 223 rem chamber. Plus your hand load is on the warm side when i look at the Hodgdon websites data. :)
 
My SIG556 Classic doesn't exhibit this problem, be it with factory ammo (Hornady, Prvi, Wolf, PMC, etc.) or reloads (LC brass, fired 2-4x). It does dent the neck pretty well, but I haven't seen any splits over several thousand rounds.
 
SigArms was friendly but curt when I talked to them on the phone this morning. Their tech support stated that using handloads voids any warranty.(says so in the manual that came with the gun). He also said the chamber is made for "positive function". To their credit they offered to "inspect" the gun. I pay shipping both ways. That is all they said.

I will ship it to them I guess.

Thanks for all your input!

Sommerled
 
I can understand the chamber being cut for "positive function" and it not being a match chamber but it shouldn't be so loose as to split all that brass. (as I'm sure you already know)
 
I wouldn't ship it back to them just yet. Paying for shipping is unacceptable. I would take a chamber casting. Cerrosafe perhaps? If it indicates the neck is too large, give them a heck of a flaming on the board. After the flames get nice and high, point corporate towards the thread. They should give you shipping to and from, and also something for your troubles. There are too many other companies that sell quality products to begin with and will fix their mess-ups no questions asked.

Here's a chart of various 223/5.56 chamber reamers. The necks run from 0.251" up to 0.2558". 0.257" for a fired case is most likely unacceptable.

http://ar15barrels.com/data/223-556.pdf
 
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I came up with an idea:

Amonia will embrittle brass on contact. If the OP used an amonia based cleaner and did not dry out the barrel extension (which is hard to do) and the brass got wet on the way in, then it is possible that necks would split especially in a hot firearm. We all know heat accelerates the reaction.

OP, did you clean with an amonia based cleaner inbetween groups?
 
Neck Diameter of a 223/5.56mm Loaded Round

Neck splits in the 223/5.56 are caused by over working the brass. I have never seen a loaded rounds neck diameter come close to the SAAMI maximum of .253" The die takes the neck down to .243" The expander opens it to .245" Loaded neck is .246" to .247" Fired necks measure .255" to .256" This is why necks like to split. Manufactures need to put more wall thickness in there brass or reduce the maximum SAAMI chamber. Bushing dies would help here. Measure your loaded rounds neck diameter. Post what you get. :)
 
To follow up: I received my rifle back from sig today. Cost me $55 in shipping.

The note attached stated that the chamber was within spec for how the rifle was designed and manufactured. They did nothing but inspect it. Their position is that it is made for "positive function" and are aware that with it's aggressive extractor it is "hard on brass". They also assured me that there is no danger at all in shooting it.

My chamber cast measured the chamber's neck at .252.

Looks like I have a brass terminator. What I will do is just use range brass and just not plan to reload it. Shouldn't be too big a deal as I have a few buckets full, however it does stink to process it for just one firing.

It is surprisingly accurate and I am satisfied with that aspect.

Thanks for all the replies!

Sommerled
 
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