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I am looking for the cause and hopefully a cure for 223 case deformation in my 196 series mini-14. Happens for both steel and brass cases. Rifle has no scope. See picture. Thanks.
Dinged in case mouths usually happen when the brass hits the charging handle/op rod assembly on the way out. Look for little brass colored impact marks on your rifle.

I wouldn't worry about the dinged cases, since when you run it through a sizing die if you reload your brass, it will force the neck back to shape. If you don't reload your spent brass, it doesn't matter at all.

Best,
Grumpy
 

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If you are shooting from a bench on a concrete slab the mouths can get dinged but not all of them. If all your brass is getting the same or similar ding then it is hitting some part of the gun when ejected. Some of your brass looks dinged on two sides which suggests it is also getting dinged when it hits the ground or walls. The case mouth is heat softened (tempered) so the neck doesn't crack when shaped. I usually partially straighten case mouth dings with a smaller diameter phillips screwdriver shaft before running them through the sizing die.
 

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High Speed Video

The only way to "see" whats happening would be to slow the ejection down using a high speed video recorder. I have a CETME that was dinging the case mouths consistently. I found a Youtube channel that had some high speed of a CETME firing and there it was. In that case (pun intended) , upon ejection the case came out at an angle aft, and the case rotated and tagged the receiver. Your image shows a very similar dinging between the cases which tells me it's striking the firearm upon ejection.
 

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Case mouth damage can occur on a firearm when the ejector is not sized properly.

When the leading edge of the ejector is too close to the chamber area it starts to put pressure on the case too early. When this happens, pressure to flip the case out of the chamber builds up and starts to distort the mouth of the case until the bolt comes back far enough for the case to clear the ejection port.

I've seen this a lot on lower quality 1911s. The fix is to take a file to the leading edge of the ejector (a little at a time) until it is not bending the cases.

I don't know that this is the issue with your Mini-14, but the theory is the same. I thought about getting a new bolt latch/ejector and seeing if I can modify it to not throw the brass so violently.
 

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that same thing happens on my mini. I totally agree with grumpy. You will see little brass marks somewhere on your receiver or handle. I was more concerned about those marks than the brass before realizing the marks would just wipe right off.
 

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It's probably hitting the charging handle. I put a recoil buffer on the rear of the recoil spring and it changed the ejection pattern higher and it stopped doing it. I reload and as others have said most of the dents come out when you resize, but not completely, but the small dents don't affect performance of the cartridge. If the mouth is deformed badly I bend it back with needle nose pliers prior to sizing. Hope this helps.
 

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Mine looked like that until I put in a smaller gas bushing. Then the problem disappeared. Whatever they were smacking into on the gun at the start of their 100' journey pretty much destroyed the case mouths. Makes me wonder if they had gotten free of the gun without hitting something if they would have been able to travel 200'.
 
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