Case head marks from AR bolt

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thesheepdog

New member
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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Alabama Shooter

New member
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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CTS

New member
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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thesheepdog

New member
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.

Sent from my HTC One X using Tapatalk 2
 
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CTS

New member
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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blfuller

New member
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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thesheepdog

New member
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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CTS

New member
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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thesheepdog

New member
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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CTS

New member
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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thesheepdog

New member
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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UtopiaTexasG19

New member
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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thesheepdog

New member
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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Alabama Shooter

New member
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.
Click to expand...

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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chris in va

New member
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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