What's causing this?

[Rembrandt]

Put together a 300 AAC, took it out for the first time today. What is causing the flattening on one side of the case mouth?

 

[beeenbag]

Does your AR have a brass deflector? This is fairly common from ARs, as the mouth of the case hits the receiver as it ejects.

You might try a heavier buffer to slow it down just a fuzz.

 

[Rembrandt]

Good call.....never noticed the brass marks till you mentioned it.

 

[AshMan40]

My 300 BLK also causes similar single flat dents in the case mouth but I've never seen two flats created. Is the second flat created by the case hitting the ground? I normally capture my brass in a brass catcher so they don't typically hit the ground.

 

[Walkalong]

Those cases are fine, and re-sizing will take care of the dings.

 

[cfullgraf]

Yes, what Walkalong said.

Sometimes if the flattening is extreme, the sizing die will crush the case mouth. If you are concerned, then use something to "expand" the mouth back to near round before running it through the sizing die.

Using a pair of needle nose pliers as a tapered expander works well to get the mouth back to near round.

 

[LRDGCO]

You should see the horror show that brass looks like after being chewed up and spat out by a PTR91. By comparison, your brass looks only slightly disheveled ;-)

 

[slowr1der]

As said, it's hitting the brass deflector on the gun on the way out. They are fine to reload. Resizing them will straighten them out.

 

[falmike]

I put a small piece of adhesive backed felt on my brass deflectors to eliminate this issue.

 

[Walkalong]

Sometimes if the flattening is extreme, the sizing die will crush the case mouth. If you are concerned, then use something to "expand" the mouth back to near round before running it through the sizing die.

Using a pair of needle nose pliers as a tapered expander works well to get the mouth back to near round.

I use this thing I found somewhere. Poke it in the case mouth and the soft brass pushes back.

 

[dh1633pm]

I use a larger than case mouth Philips head. Works for me.

 

[Blue68f100]

You can weakin the ejector spring on the bolt ( 1 coil) and greatly reduce the impact. This can happen if your over gassed too. Installing a heavy buffer and/or adj gas block to slow the bolt will eliminate the heavy banging too.

 

[drband]

I use this thing I found somewhere. Poke it in the case mouth and the soft brass pushes back.
View attachment 832778

I believe that “thing” is a plumb bob.

 

[Rule3]

I put a small piece of adhesive backed felt on my brass deflectors to eliminate this issue.

I did the same thing only a piece of that self stick velcro(loop side)

 

[Walkalong]

I believe that “thing” is a plumb bob.

If you could see it, I don't believe that would be your guess, it's very small, and that piece on the bottom is a screw, too small and too light for a good plumb bob, kind of strikes me as coming from one of those spiked dog collars. I do have a proper brass plumb bob out in the shed.

Shown next to a .32 Mag case.

 

[Galil5.56]

You should see the horror show that brass looks like after being chewed up and spat out by a PTR91. By comparison, your brass looks only slightly disheveled ;-)

Agreed, beat me to it. *IF* you can find brass from a Galil in the same zip code, it takes a much, much worse beating, along with the case sides. My Swede AG-42 Ljungman flat out crushes 6.5x55 case mouths shut, and is a real PITA to get reloadable again... It even has a rubber shell deflector as std issue for the weapon, and I use a plumb bob too, to fix things. Looking good from here Rembrandt, I kinda envy your situation.

 

[Walkalong]

My Swede AG-42 Ljungman

I'm jealous, very cool guns. You're right, they fling brass over multiple benches at the range.

 

[carbine85]

Which buffer are you using? You might consider the H2

 

[Legionnaire]

Walkalong's took is pretty neat. You can accomplish the same thing with a pair of needle nose pliers ... and they have a nice handle. When I have a case mouth that's out of round, I stick the closed pliers in, rotate 180 degrees, and voilà!

 

[Riomouse911]

H&K rifles/carbines all seem to batter fired cases to death...if they're not also fluted from the chambers as well (Mp5 for example).

My Mini-14 sends brass at least 20 feet away with every shot, that to is a real case-beater.

Stay safe!

You should see the horror show that brass looks like after being chewed up and spat out by a PTR91. By comparison, your brass looks only slightly disheveled ;-)