Please help troubleshoot spent brass.

[Mr McSimon]

I have three different questions about brass I've shot from three different guns. I have my suspicions about what's going on, and what the fixes should be (if any), but I thought I'd try to get some feedback.


This first picture is brass from my 9" .300 Blackout pistol. The load was Australian Munitions 125 grain using an A5H2 buffer. Notice the two dents on the side of the brass, consistent from round to round with 210 total fired. This was the first time I'd shot this setup.



This next picture is MEN 56 grain 5.56 out of my LE6920 using H2 buffer. Notice the odd cutout/dents on the face of the brass casing. I've shot over 1000 rounds from this gun, and this is the first time I've see the brass come out with these dents.



And lastly, also MEN 56 grain 5.56 out of a different LE6920 also H2 buffer. Oddly, the depth of the primer strike changed from round to round. Is this a primer issue or a gun issue? It's the second time I've had this gun out, low round count of about 210 fired.



All the guns fired fine, with no malfunctions. I was at an indoor range, so wasn't really able to determine the exact placement of where the spent brass was landing. I'll be doing some testing on my own tomorrow, but thought I might get a head start here if anybody has any answers.

[markm]

First pic is just the brass hitting some part of the gun on ejection. (could be whipping into the inside of the upper or some part of the outside of the upper. You should be able to see brass marks where the impact is happening.) Almost looks like the barrel extension. Not a chamber issue, or it would be scraping during ejection.

The second one is pressure signs. Swipes. Odd for MEN to do that in a COLT with a 5.56 chamber.

The last one looks like you need to replace the firing pin. You're seeing pierced primers, which likely means your firing pin is pitted/etched. This will get worse and lead to damage to the breach face on your bolt.

[TomMcC]

The only picture I would give a possible different explanation is #2. The primers don't show any real sign of pressure, but this isn't foolproof. It's a little hard to tell if it is in fact high pressure brass flow. It could be brass swipe from the ejector. Sometimes brass from lot to lot can be a little softer than another lot. Also powder can have an ever so slight difference in burn rate from lot to lot, maybe causing, and it's probably not it, a hard extraction (trying to extract while the barrel is pressurized).

I have a Bushmaster carbine that used to show those kinds of marks and just chocked it up to an over gassed gun. Now, having changed nothing except the ammo, it doesn't show the swipes anymore.

Try some different ammo and see what that does.

[markm]

Yeah. The combo of a COLT and MEN shouldn't give those ejector swipes. I'd definitely see if different ammo gave the same results.

[Mr McSimon]

That definitely puts me on the right path. I'll report back when I know more. Thanks.

[hotrodder636]

The marks on the brass in picture 1 look like feed ramp/barrel extension marks when feeding from the magazine.

[bigedp51]

Case head swipes are caused by bolt turning while the case body is still clinging to the chamber walls. This is effected by port pressure, buffer type, brass hardness and case body diameter.

The resized case body should be .003 to .005 smaller in diameter than its fired diameter. This allows the case to "spring back" from the chamber walls and extract reliably.

The punctured primer can also be caused by pushing the shoulder back too far and excessive head clearance, and using primers with a thin cup like the CCI 400



NOTE, Lake City cases are made of harder brass and I would stick with them for reloading for uniformity and durability.

[markm]

The marks on the brass in picture 1 look like feed ramp/barrel extension marks when feeding from the magazine.

I think it's dinging on extraction. Firing would push the dents back out if it were feeding. Either way, it's nothing I'd be too worried about.

[Mr McSimon]

Coming back around for an update. A new firing pin indeed fixed the punctured primers, and on visual inspection there's definitely some pitting around the shaft of the one I replaced. I've also tested Lake City brass on the other 6920 and I'm still getting case head swipes. The weapon is running fine, and you wouldn't know there was a problem if you didn't inspect the brass, but I'd like to find a fix all the same. I think I'll pick an H3 buffer and a Sprinco blue spring to see if one of those two things, or both, does the trick. I'm also still open to other suggestions.