Dented Case Mouth. What is the cause?

[rg1911]

The rifle is an Armalite AR-10 chambered for 260 Rem. I run the rifle with a TBAC silencer (hence the dirty brass).

The gas block, handguard and barrel nut had recently been removed for some maintenance work. The 'smith may or may not have gotten the gas block to align correctly with the gas port in the barrel, although he used a bore scope to align the holes.

After a PRS match, I noticed that all my cases have a small dent at the mouth. I'm assuming this happens on ejection and wonder if I'm getting insufficient gas flow and the bolt is not going all the way back. Or perhaps it's bouncing due to too much gas. Twice a round started to chamber but the previous case had not ejected completely and was caught sticking out the ejection port. (Annoying while the timer is counting down.) This was new behavior.

I'd just take it to the range and play with the SLR adjustable gas block, but the little adjustment screw head doesn't like any of the SAE or Metric hex wrenches I have and the screw is stuck, so I thought I would tap the knowledge base here while I wait for replacement parts.

Thank you,
Richard

 

[LawnMM]

Overgassed, it's hitting the ejection port as it's extracted

 

[PinesAndProjectiles]

What @LawnMM said.

 

[charnicus]

I’d say you’d be safe with upping the buffer weight. I’m running an SLR as well and needed a heavier buffer for the perfect balance. Routinely putting a drop of oil on the adjustment screw seems to help with the seizure. Periodic rotation through adjustments as well.

 

[bfoosh006]

As mentioned... bonking on the way out. And a heavier buffer should help.

Also check to see which lugs are causing your scratches at the neck. I polish even the lug by the ejection port.

As for the SLR stuck screw... flood it with Kroil at the threads.... let it soak.

The correct size should be 2MM.

 

[rg1911]

SLR is sending a replacement block since they've made changes to the adjustment screw since I bought this block. Cannot argue with that customer service. I also am thinking of fine-tuning using a heavier buffer. (I had one before getting the adjustable block, but sold it. That'll teach me.)

Many thanks for the diagnosis and the tips.

Cheers,
Richard

 

[rg1911]

Also check to see which lugs are causing your scratches at the neck. I polish even the lug by the ejection port.

As for the SLR stuck screw... flood it with Kroil at the threads.... let it soak.

The correct size should be 2MM.

I'm a trifle confused. Which lugs? Barrel extension or bolt? If the barrel extension, can you say what you used?

I have the block soaking in a carbon remover. That did the trick with another of my SLR blocks.

And you're right; 2mm is the designated size, but none of my 2mm wrenches fit; they're all too loose. The gentleman with whom I spoke at SLR this morning said some of the old ones were a little sloppy, but that the new ones all were a tight fit. At least they shouldn't strip out, especially if I work them and add a drop of oil after every range trip.

Thank you,
Richard

 

[bfoosh006]

I'm a trifle confused. Which lugs? Barrel extension or bolt? If the barrel extension, can you say what you used?

I have the block soaking in a carbon remover. That did the trick with another of my SLR blocks.

And you're right; 2mm is the designated size, but none of my 2mm wrenches fit; they're all too loose. The gentleman with whom I spoke at SLR this morning said some of the old ones were a little sloppy, but that the new ones all were a tight fit. At least they shouldn't strip out, especially if I work them and add a drop of oil after every range trip.

Thank you,
Richard

@rg1911

Sorry, I should have been more specific.

The receiver extension lugs.... I use a dremel and their felt cones w/ some metal polish.

The RE lugs are almost always sharp from the cutting, it will wear from use.. but can give feeding fits to a new AR.

Plug your chamber... the lint from the felt cones goes everywhere. Foam, cotton balls stuff like that.

And thoroughly clean the lint and polish from the RE prior to allowing the bolt to seat. The fuzz can lock up the bolt good and tight with the RE .

 

[rg1911]

@rg1911

Sorry, I should have been more specific.

The receiver extension lugs.... I use a dremel and their felt cones w/ some metal polish.

The RE lugs are almost always sharp from the cutting, it will wear from use.. but can give feeding fits to a new AR.

Plug your chamber... the lint from the felt cones goes everywhere. Foam, cotton balls stuff like that.

And thoroughly clean the lint and polish from the RE prior to allowing the bolt to seat. The fuzz can lock up the bolt good and tight with the RE .

Thank you! Shall give it a try. (Probably easier before the upper is assembled.)

Richard

 

[Herstal 12]

Who cares, it resize just fine, quit worrying about little shit like this

 

[rg1911]

Who cares, it resize just fine, quit worrying about little shit like this

No argument there. However, I prefer to adjust the rifle so it is running as close to perfectly as possible.

Richard

 

[sixtyfournmor]

You can stick a little piece of Velcro on the case deflector.

 

[rg1911]

You can stick a little piece of Velcro on the case deflector.

I've heard of that. Thanks for the reminder.

 

[brazz04]

Skip the velcro as it doesn't address the problem.

This is a simple fix, remove the ejector and spring from the bolt and cut about 2 coils off the spring. All fixed. If you're worried about messing something up, it is the same spring as is used for the detents so you may have a spare if you got some random lower parts laying around.

 

[rg1911]

Skip the velcro as it doesn't address the problem.

This is a simple fix, remove the ejector and spring from the bolt and cut about 2 coils off the spring. All fixed. If you're worried about messing something up, it is the same spring as is used for the detents so you may have a spare if you got some random lower parts laying around.

Well, I probably need to add the tool that helps to remove the ejector to my stash. (I'm sure some people can do this without the tool; I know my limitations.)

Cheers,
Richard

 

[brazz04]

Well, I probably need to add the tool that helps to remove the ejector to my stash. (I'm sure some people can do this without the tool; I know my limitations.)

Cheers,
Richard

I'm confident in you doing it as I did the same fix about two months ago on my kitchen counter lol. I have a grendel that was denting the case mouths and the guys on that forum had addressed it already, so I will step back from taking any credit for it!

 

[rg1911]

I'm confident in you doing it as I did the same fix about two months ago on my kitchen counter lol. I have a grendel that was denting the case mouths and the guys on that forum had addressed it already, so I will step back from taking any credit for it!

You're a better armorer than I, then.

 

[TonyTheTiger]

Well, I probably need to add the tool that helps to remove the ejector to my stash.

Like a small punch? Or a straight dental pick?

 

[rg1911]

Like a small punch? Or a straight dental pick?

I thought I saw an ad for a little tool that compresses the thing so some pin can be driven out, without littering the floor with tiny parts. Springs and I are not budddies.

Cheers,
Richard

 

[TonyTheTiger]

I thought I saw an ad for a little tool that compresses the thing so some pin can be driven out, without littering the floor with tiny parts. Springs and I are not budddies.

Cheers,
Richard

Never heard of such a thing but you can hook a case rim under the extractor and use it to push the ejector in.

 

[gunsnjeeps]

I cut a case head off and use a $1 C-clamp.

 

[Constructor]

Skip the velcro as it doesn't address the problem.

This is a simple fix, remove the ejector and spring from the bolt and cut about 2 coils off the spring. All fixed. If you're worried about messing something up, it is the same spring as is used for the detents so you may have a spare if you got some random lower parts laying around.

AR10 ejector springs are not the same as a detent spring