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Old January 27, 2013, 10:57 AM   #1
thesheepdog
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Case head marks from AR bolt

Hey guys,

I was shooting my AR yesterday and noticed that the case heads of my brass were getting marked/rubbed (see pic).

The BCG is brand new. The loads I shot were PPU 55gr and some mk262 clones that I handloaded.

I have an adjustable gas system too, so maybe I need to adjust the timing? The ejection was at 3:00-4:00
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Old January 27, 2013, 11:03 AM   #2
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Is that firing pin drag I see on some of the primers? That should not be in an AR.

What kind of AR did you say it was?

Also noting several different brands of ammo. Was it the same across all?
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Old January 27, 2013, 11:15 AM   #3
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The top case and the bottom two looks almost like a bulging primer to me. Either not seated properly or a little too hot a load. Are the primers slightly above the case head? What kind of recipe are you using with these?

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Old January 27, 2013, 11:18 AM   #4
thesheepdog
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The AR is a self built one. I've been building AR's for years.

All loads across the board are showing the scuff marks. It doesn't matter if it's a handload or a factory load.

I've checked all of the primers and I don't see any over pressure signs.

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Old January 27, 2013, 11:21 AM   #5
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Probably just the angle of the picture making it appear that way. Are they just scuff marks or are they actually digging into the brass?
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Old January 27, 2013, 11:23 AM   #6
thesheepdog
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Slappy, they are just scuff marks from what I can tell.

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Old January 27, 2013, 11:30 AM   #7
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This is a better picture.
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Old January 27, 2013, 12:25 PM   #8
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One thing you need to be aware of is that you should sort your brass according to head stamp. While these appear to be all WCC, some are NATO marked and some are just date stamped. Internal case volumes may vary between dates and manufacturers

You can check the weight of the case and see if there is any difference between the NATO marked and just the date marked cases. If there is, the volume may be smaller on the NATO brass.

The third case from the left of your second pic looks like a cupped firing pin indentation which would be indicative of high pressure. It is difficult to tell with a pic. Have you looked at them under magnification?

If this is happening with new factory ammo it's probably an anomaly with the new bolt and may go away after a few hundred rounds.
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Old January 27, 2013, 01:08 PM   #9
thesheepdog
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I haven't done any checking with a magnifying glass.

To my naked eye, the factory loads and the handloads all appear the same in terms of scuffing on the case head. The primers appear the same too.

I know some of you mentioned possible over pressure; I did load these hot. It's a process I've been slowly working up too over several weeks. Accuracy is excellent and I have yet to see any over-pressure signs on any of the brass.

Also, I have shot some of these hot loads in my suppressed AR and the case heads are not getting scuffed up in that one.
The brass from my suppressed AR is filthy dirty so that's how I can tell which ones were fired from which gun.

This is a new gun. I have fired around 100 rounds through it tops.
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Old January 27, 2013, 01:29 PM   #10
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Also I will add that these are CCI 400 primers; they are soft and have thin cups.
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Old January 27, 2013, 02:06 PM   #11
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I get these scuff marks when I load a little on the hot side with my .223 and 6.8. These are caused by the ejector scrubbing the case head as they are being extracted. Sometimes it is cause by incorrect timing but most often by bordering on a hot load. If their are no other pressure signs I personally wouldn't worry about it. What clock position does your rifle eject spent cases at. If 3 to 4 o'clock then it is fine and I wouldn't worry about it. If not you may try a different buffer or spring. I also wouldn't go any hotter with the load either.
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Old January 27, 2013, 02:31 PM   #12
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Slappy, I think you are correct.



Like I said, I have an adjustable gas block and it was tuned for .223 loads, not hot 5.56 loads. So I am somewhat convinced that timing my be a factor in the marred brass.
Most of the brass has been in the 3:00 position.
I also noticed that my shell deflector is taking a beating from the ejected brass as it is painted gold with brass marks.

I am running an h2 buffer.
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Old January 27, 2013, 05:58 PM   #13
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I have talked to some who believe if you don't get ejector swipes, then you aren't using enough powder.
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Old January 27, 2013, 06:19 PM   #14
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I agree hot loads are the most likely cause.
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Old January 27, 2013, 06:30 PM   #15
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Alabama,

I could agree with hot loads being the culprit but this occurs with light loads too.
The cheap .223 spec ammo I was using gets marked too.
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Old January 28, 2013, 08:25 PM   #16
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What does your extractor look like?
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Old January 28, 2013, 09:28 PM   #17
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I had the same problem using a new BCG until I took the o ring off the extractor spring and just used the spring. Check to see if your extractor has the aftermarket o ring installed.
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Old January 28, 2013, 10:21 PM   #18
thesheepdog
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Alabama, can you specify more on what you're asking?

Utopia,

I have read some on this being the cause.
I think what I'm going to do is try turning off the gas flow via the adjustable block, and double check that these cases aren't being marred by pressure.
Secondly I am going to fire some of these hot loads in my other AR, using the suspect BCG (swapping BCG's), and using the other BCG.

If the suspect BCG still has problems I am going to remove the oring and see what happens.
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Old January 29, 2013, 08:06 AM   #19
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Quote:
I think what I'm going to do is try turning off the gas flow via the adjustable block, and double check that these cases aren't being marred by pressure.
I am thinking if you are running different kinds of ammo through it with the same result it should not be a pressure problem.

I am opposed to the O ring and don't believe they are needed either. The insert and spring the way it was used for decades in the military has always worked well for me.

If that is not the issue I would check the tolerance between the extractor and the bolt face.
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Old January 29, 2013, 11:31 PM   #20
chris in va
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Just an uneducated guess...

The bolt rotates, right? I'm guessing the case is stationary while the bolt is rotating, causing the scuffs.

Perhaps it's a bit overgassed so the bolt is unlocking while the case is still 'glued' to the chamber.
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Old January 30, 2013, 12:30 AM   #21
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The striker indents appear to be wanting to reverse flow. Normally the M16 requires a very hard striker indent to reliable ignition which comes with deeper fired primer indents. If the hammer spring is not up to spec the pressure rises, allowing the striker to head in the other direction. I had this bad on my 7615 and checked the striker energy and it was too low. I replaced the hammer spring with new Wolf spring and the indents now look correct.

This is normally tested by measuring the depth on a pressure copper in a copper holder that looks similar to a headspace gage. The SAAMI standard for 223 now is .016" indent depth and was .020". The M16 spec calls for .022" indent. The hardest primer to ignite in US inventory is Cal 50 followed by primers for 5.56MM.
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Old January 30, 2013, 07:26 AM   #22
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Appears to me that brass has two opposing burnish marks on the outside rim. Neither looks like
ejector cutout. The primers look "unremarkable" (as doctors say)

Instead, the burnish marks appear consistent with a possible uneven bolt face that scrapes the case (which has
stretched back to meet it on firing) upon opening rotation.

- Are you able to confirm that the bolt face is totally flat?
- (Since you build ARs) do you have another bolt that would give you acceptable headspace to try out?

Last edited by mehavey; January 30, 2013 at 11:28 AM.
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Old February 3, 2013, 12:14 PM   #23
thesheepdog
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Okay guys I did a little test.

Using 5.56 NATO ball ammo and my handloads loaded to NATO pressures, and using different guns, the marks still show up, both guns.

I even turned down the gas on both guns and that didn't change anything.

I think the ammo is just hot but not dangerous.
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Old February 5, 2013, 08:42 PM   #24
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The first pic looked like crappy handloads the second pic looked fine to me.
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Old February 6, 2013, 10:07 PM   #25
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3 of those cases look like they have pull marks.
If so, that is a sign of too much gas.

Read this:
www.ar15barrels.com/prod/operation.shtml

Then look at the cases from the other side and see if there are pull marks on the rims.

Also, how many firings are those cases?
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