Inspecting once fired LC 5.56 / rings on base of brass???

[Coach Z]

I purchased 1k once fired Lake City 5.56 brass partly for my AR and partly to make some 300 brass from it. First I was surprised at how freaking dirty this stuff was. I was also really happy with how clean this stuff came after wet tumbling with stainless pins!

My question is that some of the brass has a shiny ring between .22 and .23 up from the bottom of the case. I ran a pick down the inside of the case and there is no discernible bump or edge at all. I measured the length of 10 random cases to see if they seemed to be stretched and the average length of the ones I measured was 1.7552" I've been reloading pistol for a while now but just getting started on rifle so I'm not sure how this compares to "normal"

I've separated out the cases that have this ring and if it keeps going at this rate it will be about 15% of the total. I've pasted three pics below first two are before and after the wet tumbling and the last one is a shot of the shiny ring around the base.

All advice on the matter would be appreciated.

 

[Marco Califo]

They look fine after the cleaning. Looks like the primer crimp is gone so I think the shiny area was from someone handling the case to remove the crimp. Load them.

 

[Coach Z]

No they're definitely crimped. I deprimed them before tumbling so the primer pockets got cleaned as well.

That same ring on 40 cases so far has me just a wee bit paranoid.

 

[Bart B.]

That ring 2/20ths inch or so in front of the case head is normal; happens all the time. It happens because the case wall thickness behind it isn't thin enough to get pressed against the chamber wall at peak pressure. All the case forward from it got pressed out against the chamber and didn't spring back to original diameters.

It's called the pressure ring. The thicker the brass, the less it will be visible. Lower peak pressures lessens it, too.

Brass there will thin too much if the case is full length sized to set the fired case shoulder back more than .003" a few times. Use a case gauge to measure cases headspace to see what's happening when they're resized.

 

[Coach Z]

Just found one that was pretty dramatic. The base measures .3758" and the bulge measures .3797"

 

[Jim243]

The cases look fine. The reason the back of the case is smaller than the rest of the case is due to the "BOLT", it appears that the internal dimensions between the bolt face and the locking lugs is causing that while the internal dimensions of the chamber are a bit more generous than the inside of the bolt.

Using a X-Base full length re-sizing die will put the case back into spec.

Take the case and insert it onto the bolt face and you should see that the ring should disappear from view.


Jim

 

[Bart B.]

Jim, all the bolt head diameters on my rifles 2/10" forward of its face inside the shroud are several thousandths larger than both the case pressure ring diameter as well as the chamber at that point. Some bolts have no shroud at all forward of their face past the case rim and 95%+ of the case from head to pressure ring can bee seen; it's not supported in any way.

Bolt shrouds around the rear 2/10" of the case do not touch the case much at all from expansion due to peak pressure in the case. They're made large enough to allow for small misalignment of bolt axis to chamber axis.

Measure your bolt shroud inner diameters then compare them to chamber diameters 2/10" forward of the breech face point.

Here's a picture of a Model 70 bolt head with a .308 Win case held in it against the bolt face. Note the barely visible case pressure ring at the arrow and none of the case back of that is supported by anything. The barrel is coned at its back several thousandths forward of the locking lug angled part. The pressure ring on the case is almost 1/8th inch forward of where the back of the chamber ends at that coned area right at the front edge of the extractor groove.

 

[Jim243]

Bart: If I had to guess, he has an AR bolt carrier group from one mfg and a barrel from a different one. Then again it might not have been from his gun, but someone else's. But was definatly from an AR-15 so what does a 308 bolt action rifle have to do with this post??

Jim

 

[Coach Z]

Guys this is all once fired brass from a military range. Could be m4's SAW or a mix of who knows what. I don't have any way of verifying its pedigree if you will so I just wanted to make sure I wasn't setting up for a disaster.

 

[Jim243]

Coach, there are no guarantees in life. But if it was from a Mil range with the primers still in them and crimped then it is once fired brass and should not be a problem.

If you feel uncomfortable using them then just toss the cases that are like that. If X-Small Based re-sized they should look like normal cases again.

Jim

 

[Bart B.]

Jim, I used that picture to show how the back 2/10ths if a case is unsupported and does not touch a chamber wall anywhere where the case diameters are smaller than from the pressure ring forward. This is normal with virtually all rimless cases.

 

[Metal god]

They look good to me . Well that case in post #5 is a little bulby . That case would likely be fine but when I run into things like that I set those cases aside and place in my SHTF pile . I Use once fired brass a lot and if there is anything that looks odd but I think it would still work . I put those cases aside for a just in case type of thing .

I have 4 loads on some cases that looked just like your first pics . They still look good and I plan to load them again .

 

[Bart B.]

MG, I've never heard a very normal looking pressure ring called 'bulby." Maybe we could get SAAMI to add 'bulby' to its glossary.

99% or more of the new, rimless bottleneck cases I've shot in bolt action and semiauto rifles look the same. Even thick wall arsenal match cases. Very reduced loads didn't have that bulge. Cases with a big spread in wall thickness had no bulge on the thick part but a prominent bulge opposite that on the thin side.

None got reduced to disappear when full length sized. Just less pronounced. Depending on the brass texture and the viewing and light source angle, a given difference in case head and pressure ring diameters will appear more or less bulby.

 

[Metal god]

MG, I've never heard a very normal looking pressure ring called 'bulby." Maybe we could get SAAMI to add 'bulby' to its glossary.

lol yeah when the spell check did not have a word for it , I knew I had created a new word I'll call SAAMI

As for the rest , yep I agree . I was just telling the OP what I do when I see something odd with a case .