Rough Chamber Neck

[m12lrs]

Guys I have an interesting problem. I recently purchased a premium barrel from a well respected source that will remain unnamed. I know they would take the barrel back and replace it but being the do-it-yourselfer I am I want to fix it myself.

Now this is an AR-15 so please don't lose interest. It is still a barrel. First time I fired it it just locked up tight. Had to remove the lower and tap the bolt carrier to get it to unlock. I took it back home and checked it with the go/no go gages and everything was good. Checked the bolt and extractor and everything was good.

Looking at the brass I noticed two long scratches on the neck (see pic below). I suspicioned a bur in the neck. well that gave me an excuse to buy me a new toy. Got the new Lyman borescope. now my pics are not the best. It has a really clear view but every time I moved to hit the capture button I got them a little out of focus. I still think you can see what I believe is my problem. I assume that the ridge in the chamber and the bur are where the reamer stopped when they were chambering it.

I ordered a couple of flexi hones that are about 10 thousands larger than what saami says the neck should be and plan to polish up just the neck. Got the 400 and 800 grit. Figured I would polish a little bit and take a look and repeat till its smooth. Flex-Hone®, Cross Hole Deburring, Ball Hones

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[earl39]

I just got my barrel from a name brand and it had the smallest gas port hole the chart called for. Would not unlock the bolt. Drilled it out to a #41 which is the next to smallest for a rifle gas system and it started working fine. As for the scratches have you chambered a round and then extracted it without firing? Do this carefully and see if the scratches are still there. If so i would do what it takes or send the barrel back to be fixed. Make sure it is not being scratched by the lugs in the barrel extension. If no scratches then check to see what size the gas port is. There is a chart for port size to position of port here http://www.tacticalmachining.com/lea...ort-sizes.html

[m12lrs]

I just got my barrel from a name brand and it had the smallest gas port hole the chart called for. Would not unlock the bolt. Drilled it out to a #41 which is the next to smallest for a rifle gas system and it started working fine. As for the scratches have you chambered a round and then extracted it without firing? Do this carefully and see if the scratches are still there. If so i would do what it takes or send the barrel back to be fixed. Make sure it is not being scratched by the lugs in the barrel extension. If no scratches then check to see what size the gas port is. There is a chart for port size to position of port here http://www.tacticalmachining.com/lea...ort-sizes.html

it wasn't the gas port size or the setting on the adjustable gas block. A gorilla could not have pulled back he charging bar after firing a round. I had to take off the lower and take a punch and hammer and knock the back of the bolt carrier a few whacks to break it loose.

[RC20]

I do think its good information to share so thank you.

I would suggest getting a small brass rod to kick shells out of the chamber if need be.

Also would send it back but if you don't, good luck with the repair and let us know.

I do

[m12lrs]

I do think its good information to share so thank you.

I would suggest getting a small brass rod to kick shells out of the chamber if need be.

Also would send it back but if you don't, good luck with the repair and let us know.

I do

I will keep everyone posted on how it turns out. Hate to trash a $600 barrel but I think I will be successful.

Have a cut rifling Satern barrel on order if they will ever make it.

[Robinhood]

That bore looks like something is wrong. I would pull the barrel and polish the edges of the bolt locking lugs in the barrel nut(extension). When the case is getting extracted it can drag across the sharp edges and leave deep scrapes.

[earl39]

As you said the pictures are a little out of focus but the middle one shows a slight ridge right at the rifling. That is in the freebore area and will not have effect on the brass. The other two i can't determine exactly where the burr is in relation to the chamber. That said it is your barrel if you want to try to polish it out go for it.
Back to had to hit the bolt carrier to get it to unlock, did you pull the charging handle and slam the butt of the rifle on the ground to try to get it to unlock? That is the common and accepted way to clear the weapon when it won't unlock before going to more extreme measures. The scratches on the brass really look like they are made by the locking lugs in the barrel extension BUT with the two photos not being clear in relation to position you can't rule anything out yet.
Just wondering what your experience level with the AR platform and trouble shooting is?

[m12lrs]

As you said the pictures are a little out of focus but the middle one shows a slight ridge right at the rifling. That is in the freebore area and will not have effect on the brass. The other two i can't determine exactly where the burr is in relation to the chamber. That said it is your barrel if you want to try to polish it out go for it.
Back to had to hit the bolt carrier to get it to unlock, did you pull the charging handle and slam the butt of the rifle on the ground to try to get it to unlock? That is the common and accepted way to clear the weapon when it won't unlock before going to more extreme measures. The scratches on the brass really look like they are made by the locking lugs in the barrel extension BUT with the two photos not being clear in relation to position you can't rule anything out yet.
Just wondering what your experience level with the AR platform and trouble shooting is?

I tried the usual technique. Pull charging handle? A gorilla couldn't budge it. Slam stock down? No effect. It took about 3 raps with a hammer and brass punch on the back of the bolt carrier to dislodge it.

The ridge you see with the bur in it runs all the way from the beginning of the rifling to the start of the shoulder. I assume it is where they stopped the reamer during chambering. that worst area with the bur in it is just about the middle of the neck. You can see it in all three pics from rifling to shoulder.

Can't hurt to smooth out the reamer marks. If that doesn't fix it I will move on to the next thing.

I have built a few.

I don't understand how the locking lugs could have marked the neck of the brass. The round was single loaded into the chamber not the magazine and was most definitely not ejected from the chamber but slowly pulled out by hand.

[earl39]

I don't understand how the locking lugs could have marked the neck of the brass. The round was single loaded into the chamber not the magazine and was most definitely not ejected from the chamber but slowly pulled out by hand.

And this is information that was not in the original post and changes how we all look at the pictures and what is suggested. Thx for clearing that up.

[sharpshooter]

The scratches are happening at extraction. When the case clears the chamber mouth, the ejector slams it to the side, wedging the neck between 2 of the lug abutments. The lug abutments have a sharp edge on the inside, allowing the brass to dig in. This is not causing an extraction problem as it is after the fact. I can't tell anything from the pictures.......the Lyman borescope has the same video quality as the audio quality of an RCA Victrola.

[m12lrs]

The scratches are happening at extraction. When the case clears the chamber mouth, the ejector slams it to the side, wedging the neck between 2 of the lug abutments. The lug abutments have a sharp edge on the inside, allowing the brass to dig in. This is not causing an extraction problem as it is after the fact. I can't tell anything from the pictures.......the Lyman borescope has the same video quality as the audio quality of an RCA Victrola.

I don't understand how the locking lugs could have marked the neck of the brass. The round was single loaded into the chamber not the magazine and was most definitely not ejected from the chamber but slowly pulled out by hand.

[eddiesindian]

had more or less the same problem with one of my LR308s. Bore scoped it, and knew full and well what the problem was. Tight, poorly cut chamber. I had 2 options. !. Buy a reamer, use it once for the cleaning...or 2.polish the living crap out of it using several mops coated with course,med,fine lapping compounds then with jewelers compound. I chose #2. it worked.
Happy to say, I sold "that" gas gun and purchased a Savage Bolt gun.

[m12lrs]

had more or less the same problem with one of my LR308s. Bore scoped it, and knew full and well what the problem was. Tight, poorly cut chamber. I had 2 options. !. Buy a reamer, use it once for the cleaning...or 2.polish the living crap out of it using several mops coated with course,med,fine lapping compounds then with jewelers compound. I chose #2. it worked.
Happy to say, I sold "that" gas gun and purchased a Savage Bolt gun.

I have the Savage bolt guns too!

Like playing with all of them.

I believe I can make this work. First idea was exactly what you did. Bore mops.and lapping compound. But I believe this flex hone will work better. I have checked headspace with the Amax 123 and I have about 10 thousands of freebore.

If not I have a satern cut rifling barrel on order. **** shame to junk a $600 barrel though.

This one is a lightweight Grendel. My plan is a thermal scope hog hunting gun. We will see how it goes when the hones come.

[gbflyer]

I can certainly appreciate wanting to do it yourself. But I think if I paid 6 Benjamin's it would be in the mail back to the source before I'd use a cylinder hone. Could be that your fix works out fine, hope it does!

[sharpshooter]

I don't understand how the locking lugs could have marked the neck of the brass. The round was single loaded into the chamber not the magazine and was most definitely not ejected from the chamber but slowly pulled out by hand.

It's not the locking lugs...it's the lug abutments in the barrel extension. Soon as the neck of the cartridge clears the chamber mouth, the ejector pushes it against those sharp lug abutments. Makes no difference whether it happens slow or fast.

[earl39]

m12lrs It would seem there are a lot of things you don't understand about the problem you are having with your build but one thing shows up repeatedly and that is the fact you came here asking for help and with an answer already formed and when the answers you got were not what you wanted they had to be wrong. If you feel our answers are wrong then i suggest you go to one of the AR or Grendel forum and ask the same questions. Maybe even copy and paste and see what the answers you get are. If you paid 600 for a Grendel barrel and want to grind/hone on the chamber and ruin any warranty you might have on it then by all means go for it.
Your adjustable gas block is to reduce the gas pressure and it can only reduce what it is supplied with. If it doesn't get enough gas then no matter how open you set it you will not get your bolt to unlock. The design of the AR is such that with the proper amount of gas pressure you never have a failure to unlock. You may rip the lip off the cartridge or even cause the case to separate but the bolt will unlock unless there is a gas leak somewhere. The gas system pushes in two directions to unlock the bolt. OH the heck with all this i am not going to waste my time and the time of anyone reading this trying to explain something to someone that has already decided what they think is the only way things can be and everyone else is wrong. I can with a large amount of certainty state you are undergassed. Did the scratches come from the chamber? I doubt it because if you look at your own pictures you have a scratch in the shoulder as well and it lines up with the scratch on the neck which has two scratches on it which are the same distance apart as the lug abutments (what the locking lugs on the bolt lock against in the barrel extension when in battery). Is your chamber perfect? NO Is your chamber bad enough to cause problems? I can't say for certain. Should your chamber be fixed? If it worries you send it back and have the maker fix it or at least look at it. If you want to throw away 600 bucks send me the barrel as is and i will run it on one of my uppers. If you want to cause more problems than you already have then hone away and remember if you change the shape of the chamber you can cause more problems than you have now and have no recourse as to getting it fixed. Setting back an AR barrel is next to impossible.

Rant over

[m12lrs]

m12lrs It would seem there are a lot of things you don't understand about the problem you are having with your build but one thing shows up repeatedly and that is the fact you came here asking for help and with an answer already formed and when the answers you got were not what you wanted they had to be wrong. If you feel our answers are wrong then i suggest you go to one of the AR or Grendel forum and ask the same questions. Maybe even copy and paste and see what the answers you get are. If you paid 600 for a Grendel barrel and want to grind/hone on the chamber and ruin any warranty you might have on it then by all means go for it.
Your adjustable gas block is to reduce the gas pressure and it can only reduce what it is supplied with. If it doesn't get enough gas then no matter how open you set it you will not get your bolt to unlock. The design of the AR is such that with the proper amount of gas pressure you never have a failure to unlock. You may rip the lip off the cartridge or even cause the case to separate but the bolt will unlock unless there is a gas leak somewhere. The gas system pushes in two directions to unlock the bolt. OH the heck with all this i am not going to waste my time and the time of anyone reading this trying to explain something to someone that has already decided what they think is the only way things can be and everyone else is wrong. I can with a large amount of certainty state you are undergassed. Did the scratches come from the chamber? I doubt it because if you look at your own pictures you have a scratch in the shoulder as well and it lines up with the scratch on the neck which has two scratches on it which are the same distance apart as the lug abutments (what the locking lugs on the bolt lock against in the barrel extension when in battery). Is your chamber perfect? NO Is your chamber bad enough to cause problems? I can't say for certain. Should your chamber be fixed? If it worries you send it back and have the maker fix it or at least look at it. If you want to throw away 600 bucks send me the barrel as is and i will run it on one of my uppers. If you want to cause more problems than you already have then hone away and remember if you change the shape of the chamber you can cause more problems than you have now and have no recourse as to getting it fixed. Setting back an AR barrel is next to impossible.

Rant over

Well rant on

I will be sure and let you know how it turns out

Don't think I am not listening

But I don't believe polishing that neck a touch will hurt it a bit. Fact is the same company is selling a chamber hone just to clean the crud out of your rifle chamber. I will mask off all of the hone except for the very end the length of the neck of my brass. Use the tape as.a false shoulder to set.the depth. I think I have.it figured out. I know that neck is rough. I know smoothing it out is a good thing. A few seconds and then check it with the borescope. Repeat until success.

http://ads.midwayusa.com/product/176...rVMaAqYk8P8HAQ

http://www.brownells.com/gunsmith-to...m-prod651.aspx

[Robinhood]

The scratches are happening at extraction. When the case clears the chamber mouth, the ejector slams it to the side, wedging the neck between 2 of the lug abutments. The lug abutments have a sharp edge on the inside, allowing the brass to dig in. This is not causing an extraction problem as it is after the fact.

Looks like a duck. Quacks like a duck

[Steelhead]

It's not the locking lugs...it's the lug abutments in the barrel extension. Soon as the neck of the cartridge clears the chamber mouth, the ejector pushes it against those sharp lug abutments. Makes no difference whether it happens slow or fast.

This.

[m12lrs]

And.this caused the brass to stick in the.chamber?

He'll you should be able to cut the gas off completely with the adjustable gas block, fire.a round.and cycle the action with the charging handle

Obviously sharpshooter believes you just open up the.gas till it.cycles or rips.the.case head off and keep shooting until the fired brass smooths out the chamber walls.

The pics of.the chamber neck mean nothing.

[Robinhood]

Is it possible there are 2 issues, a case/pressure/sizing issue or some other chamber problem, and the marks are left by the ejection? I have seen gas guns rip the rims off of cases due to over pressure.

[m12lrs]

Is it possible there are 2 issues, a case/pressure/sizing issue or some other chamber problem, and the marks are left by the ejection? I have seen gas guns rip the rims off of cases due to over pressure.

look at the beginning of the thread. An explanation in pictures. the debate about the scratches on the brass doesn't have anything to do with the real problem

[Robinhood]

look at the beginning of the thread. An explanation in pictures. the debate about the scratches on the brass doesn't have anything to do with the real problem

Looking at the brass I noticed two long scratches on the neck (see pic below). I suspicioned a bur in the neck.

I stand corrected. The title of the thread threw me, "Rough Chamber Neck". I also had the part about the hones to clean up something running through my head. You can see where I got confused.

[eddiesindian]

I have the Savage bolt guns too!

Like playing with all of them.

I believe I can make this work. First idea was exactly what you did. Bore mops.and lapping compound. But I believe this flex hone will work better. I have checked headspace with the Amax 123 and I have about 10 thousands of freebore.

If not I have a satern cut rifling barrel on order. **** shame to junk a $600 barrel though.

This one is a lightweight Grendel. My plan is a thermal scope hog hunting gun. We will see how it goes when the hones come.

I don't think you need to junk the barrel. 6 bills is ahole lotta cash. Id think about sending it back. If not, clean the chamber as best you can. After all?....it is your barrel and you can do with it as you please. Good Luck

[earl39]

1...He'll you should be able to cut the gas off completely with the adjustable gas block, fire.a round.and cycle the action with the charging handle

2...Obviously sharpshooter believes you just open up the.gas till it.cycles or rips.the.case head off and keep shooting until the fired brass smooths out the chamber walls.

3...The pics of.the chamber neck mean nothing.

1...Some will some won't.

2...Sharpshooter never said over gas the action nor did I. I said a properly gassed system will unlock.

3...If the pics of the chamber neck mean nothing then why did you put them up there? And if the scratches on the neck have nothing to do with the real problem why even post the pics of the brass?