Dented case mouth

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Longnkrnch

New member
My nephew purchased a CMMG .300 Blackout. He has tried a few different types of ammo (factory loads) and they all do the same thing. Once fired, the ejected case is bent in slightly at the case mouth. The gun shoots fine and is very accurate. Anyone ever experienced this?
 
If you reload, this will not be a problem. The dent will go away when resized. If you do not reload. Well it ain't a problem anyway. It is caused by the case mouth contacting the ejection port on the way out. Cut a couple of coils off the ejector spring, and this will probably go away.

JD
 
Originally Posted By: LongnkrnchMy nephew purchased a CMMG .300 Blackout. He has tried a few different types of ammo (factory loads) and they all do the same thing. Once fired, the ejected case is bent in slightly at the case mouth. The gun shoots fine and is very accurate. Anyone ever experienced this?

There is a is a small lump of metal just behind the ejection port that is there to deflect cases so they don't hit you... t is called a case deflector. Normally, it puts a light dent just behind the shoulder of the 223 case, but because the case of a 300 BLK is shorter, the dent forms at the mouth.

It is no problem, just make sure (if you reload) that you remove the dent before seating a bullet. Most dies will remove the dent, but you can also use a Lyman "M" die (short) to do it.


 
My 1911 does this, sometimes not at all and sometimes the dent is severe enough I have to massage it out before it gets resized or else it gets trashed. For mine it's a timing issue with the extractor, it's pivots the brass before it has fully cleared.

No worries after it's sized though.
 
Put a small piece of stick on felt on the case deflector and it will help. I did this for a little while and it made the dents a lot less noticable.
 
Thanks for all the info. Let me make sure I understand. During ejection the case is turned 180 degrees very quickly and the case mouth is striking the case deflector?
 
Originally Posted By: LongnkrnchThanks for all the info. Let me make sure I understand. During ejection the case is turned 180 degrees very quickly and the case mouth is striking the case deflector?

Yes, exactly.

Some guys put a small piece of rubber on the case deflector with an adhesive like the poster above said.

.

 

As stated, not a problem, and there are solutions. As cat
mentioned, the case deflector is the cause. I have taken
black tool handle dip(makes a plastic coating on tool
handles), and painted a layer or two on the face of the
case deflector. I have a custom AR-15, with a wildcat
chamber, so every piece of brass is formed, and neck turned.
I DON'T LIKE DENTS IN THESE CASES. The tool handle dip
helped a bunch.

Squeeze
 
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