Chamber debris

[Jeff A]

I have a problem with an AR-15 upper that I built. The Krieger barrel is chambered in 6.5 Grendel. I found that it is damaging cases like the case pictured here.

The barrel has 127 rounds down it and I believe that it started doing this half way through a box of factory Hornady ammo that I used for barrel break in. I looked at the chamber with my Borescope and found a collection of brass at the point on the shoulder that would correspond to this damage which occurs on every case. I was able to clean the brass out of the chamber but there appears to be some metal that I cannot remove right at this spot at the beginning of the shoulder. I used a wire chamber brush but this debris is still there. I would like to get it out without removing the barrel, but if anyone has some good ideas, I’m listening.

 

[CatShooter]

I have a problem with an AR-15 upper that I built. The Krieger barrel is chambered in 6.5 Grendel. I found that it is damaging cases like the case pictured here.

The barrel has 127 rounds down it and I believe that it started doing this half way through a box of factory Hornady ammo that I used for barrel break in. I looked at the chamber with my Borescope and found a collection of brass at the point on the shoulder that would correspond to this damage which occurs on every case. I was able to clean the brass out of the chamber but there appears to be some metal that I cannot remove right at this spot at the beginning of the shoulder. I used a wire chamber brush but this debris is still there. I would like to get it out without removing the barrel, but if anyone has some good ideas, I’m listening.

Soak a piece of cloth with bore cleaner (KG-12 comes to mind) and let the chamber soak for a day or two.

 

[fdshuster]

Any chance the brass debris is being ripped off the cases as they are fed into the chamber? You may have some sharp edges somewhere.

Use the borescope to look for brass rub marks on the locking lugs, mouth of the chamber, etc.

 

[Jeff A]

I have a problem with an AR-15 upper that I built. The Krieger barrel is chambered in 6.5 Grendel. I found that it is damaging cases like the case pictured here.

The barrel has 127 rounds down it and I believe that it started doing this half way through a box of factory Hornady ammo that I used for barrel break in. I looked at the chamber with my Borescope and found a collection of brass at the point on the shoulder that would correspond to this damage which occurs on every case. I was able to clean the brass out of the chamber but there appears to be some metal that I cannot remove right at this spot at the beginning of the shoulder. I used a wire chamber brush but this debris is still there. I would like to get it out without removing the barrel, but if anyone has some good ideas, I’m listening.

Soak a piece of cloth with bore cleaner (KG-12 comes to mind) and let the chamber soak for a day or two.

Thanks. I'll try it

 

[Jeff A]

Any chance the brass debris is being ripped off the cases as they are fed into the chamber? You may have some sharp edges somewhere.

Use the borescope to look for brass rub marks on the locking lugs, mouth of the chamber, etc.

Afraid not. When I built this upper I did a polish job on the barrel extension before it was attached to the barrel. With the borescope, you can see the piece of metal that is causing this.

 

[jonbearman]

I think a light polish of the chamber may be necessary.

 

[amlevin]

It would appear that this is a great example why one should use a bore guide while cleaning.

It's very possible that the end of a cleaning brush or cleaning rod has nicked the shoulder area of the chamber.

May have to go chasing this "piece of metal" with some 2,000 grit wet/dry attached to the end of a piece of doweling shaped to the same angle as the shoulder.

Here's a chamber drawing to help you with the angle. 30 degrees for the shoulder angle.

http://img232.imageshack.us/img232/2082/grendelchamberpage001.jpg

Another way to deal with this would be to just point a hardwood dowel at the shoulder angle and attempt to work the metal piece out using J-B bore cleaner and/or Bore Bright.

Harder the dowel the better. Maybe even a metal rod turned on a lathe.

Another "field expedient" might be to take one of the damaged cases, f/l size it, drill out the primer pocket, and attach the case to a long piece of all thread. Thread the hole in the case head and secure with a lock nut. Put some fine compound (like scope lapping compound) on ht the case shoulder and lap out the high spot or piece of metal that's stuck there. Slow and patient should do the job without having to find the reamer that cut the chamber to begin with.

 

[CatShooter]

It would appear that this is a great example why one should use a bore guide while cleaning.

It's very possible that the end of a cleaning brush or cleaning rod has nicked the shoulder area of the chamber.

May have to go chasing this "piece of metal" with some 2,000 grit wet/dry attached to the end of a piece of doweling shaped to the same angle as the shoulder.

Here's a chamber drawing to help you with the angle. 30 degrees for the shoulder angle.

http://img232.imageshack.us/img232/2082/grendelchamberpage001.jpg

Another way to deal with this would be to just point a hardwood dowel at the shoulder angle and attempt to work the metal piece out using J-B bore cleaner and/or Bore Bright.

Harder the dowel the better. Maybe even a metal rod turned on a lathe.

Another "field expedient" might be to take one of the damaged cases, f/l size it, drill out the primer pocket, and attach the case to a long piece of all thread. Thread the hole in the case head and secure with a lock nut. Put some fine compound (like scope lapping compound) on ht the case shoulder and lap out the high spot or piece of metal that's stuck there. Slow and patient should do the job without having to find the reamer that cut the chamber to begin with.

It is not a nick in the chamber - it is a piece of brass stuck to the wall. It is easy to see by the shape of the mark in the case. I have seen hundreds of these over the years.

The end of a brush (brass/bronze) cannot "nick a chamber".. it is not metallurgicaly possible. Soft metals do not damage harder metals.

And to using an abrasive paste... that will do nothing.

The most aggressive anyone should get with a chamber is a wood, or brass rod.

 

[Jeff A]

It would appear that this is a great example why one should use a bore guide while cleaning.

It's very possible that the end of a cleaning brush or cleaning rod has nicked the shoulder area of the chamber.

May have to go chasing this "piece of metal" with some 2,000 grit wet/dry attached to the end of a piece of doweling shaped to the same angle as the shoulder.

Here's a chamber drawing to help you with the angle. 30 degrees for the shoulder angle.

http://img232.imageshack.us/img232/2082/grendelchamberpage001.jpg

Another way to deal with this would be to just point a hardwood dowel at the shoulder angle and attempt to work the metal piece out using J-B bore cleaner and/or Bore Bright.

Harder the dowel the better. Maybe even a metal rod turned on a lathe.

Another "field expedient" might be to take one of the damaged cases, f/l size it, drill out the primer pocket, and attach the case to a long piece of all thread. Thread the hole in the case head and secure with a lock nut. Put some fine compound (like scope lapping compound) on ht the case shoulder and lap out the high spot or piece of metal that's stuck there. Slow and patient should do the job without having to find the reamer that cut the chamber to begin with.

I have and use a JP cleaning rod guide. Would not be without it. Not a "nick" as viewed with the borescope. I do like the wood dowel idea. Will work on that.