Hi, all!

I got a RRA NM rifle still new w/ about 200 rounds through it.  When I was going over the rifle, I noticed that bolt carrier is shaving some portion of upper receiver's interior wall.  Even though I only shoot 200, I do lot of dry fire practice for aiming & position.

A picture could tell the whole story much faster but let me see if I can explain.
On upper receiver's interiror wall, if you see through the ejection port (on the opposite side), there is a small vertical cylinderically machined portion in interior wall where bolt carrior moves back and forth.  Due to the vertical clyinderical machining, there is a discontinue of interior wall.  Since bolt carrier's overall diameter is small than upper receiver's internal wall, I guess bolt carrier could be cockeyed while moving & catch that discontinued portion of inteiror wall created by vertical clyinderical machining.

Bolt carrier has 4 smooth rails machined that slide against upper receiver's interior clyinderical wall.  It seems that bolt carrier's upper left rail (while holding rifle as you would shoot) leading edge is catching the disconnected interior wall of upper receiver.  Bolt carrier's rail machining seems perfectly fine and I could smooth out the rail's leading edge w/ Dremel.  

I'm sorry for this long & wordy explanation but should I be worried about interior wall being shaved by bolt carrier?  Is this normal break-in?  I still see the shaving is happening and interior wall's black finish is shaved away and shaved portion is getting bigger.

Thanks,

Matt.

that is a wordy explanation............. whew.


sometimes it happens, it needs to mate or wear in. if there is a nick in the carrier maybe rounding it off will help, I say post a pic before so we can determine if it is ok.

Normal wear in.
here is mine...

so is it shaving it down to bare alumn?

Quoted: that is a wordy explanation............. whew. sometimes it happens, it needs to mate or wear in. if there is a nick in the carrier maybe rounding it off will help, I say post a pic before so we can determine if it is ok.

I had a hard time to post pictures previously...
Speaking English as my second language caused those long~ & wordy descriptions...

Quoted: so is it shaving it down to bare alumn?

Yes, just like the picture above...the black finish is shaved away and there are still some bare aluminum shaved.  Based on the picture above, I guess I will see more shavings...

now cb1's upper probably has tons of ammo down it and THAT would be normal. A just purchased carbine should not to it at all. take that burr and polish it off if you can, can you post a pic of it? I am very anxious to see it after that last statement.

some of my uppers on the inside have "wear" marks from extensive use.
none however are "shaved"




maybe its just worn?

Quoted: Quoted: Quoted: that is a wordy explanation............. whew. sometimes it happens, it needs to mate or wear in. if there is a nick in the carrier maybe rounding it off will help, I say post a pic before so we can determine if it is ok. I had a hard time to post pictures previously... Speaking English as my second language caused those long~ & wordy descriptions...hr What's your first language? if it is spanish perhaps i can help you out on how to post a picture, just IM me, mmmmmkay? HUNTER.

Hunter, thanks for offering your help.
I wish I could pick up Spanish as my third language!  One of my brother-on-laws is from Mexico.  His English is extremely good though...

I'm from Korea.

Matt.

Quoted: now cb1's upper probably has tons of ammo down it and THAT would be normal. A just purchased carbine should not to it at all. take that burr and polish it off if you can, can you post a pic of it? I am very anxious to see it after that last statement.

OK, finally figured out how to make a link to photo pages.  I tried to pull pictures directly here but it didn't work as I intended.

For my rifle & bolt carrier shaving pictures, please click here!

Thanks for looking.
Matt.

My 20" Bushmaster has the same markings in just about the exact same areas. Mine has probably 150 rounds through it.

Oh... The wear is in the area where the bolt cam moves in and out.  I believe that wear is completely normal (mine look that way).

I just looked at the pictures.
for a new rifle that looks extreme. the picture I posted has about 10.4K through it at the time of the picture.

I would bet there is a bur of metal on the carrier causing it. a little polishing should knock that out.

ETA: the wear around the cam pin cut out is normal. the scratch going down the upper is from the carrier wearing in it's travel path.

Funny how life repeats itself.  Here is my thread regarding the identical problem.

www.ar15.com/forums/topic.html?b=3&f=66&t=247392

and here is my new upper after just 50 rounds.

Make sure the FP retaining clip is inserted in the  carrier all the way.

Tag.

I'll have to take a pic that you guys will shit over from my M&A parts upper tomorrow.

WIZZO

I'm no AR Doctor, but my Bushy did that.  Alot of others have mentioned similar things.  As someone put it to me, the bolt carrier is just making a home.

Quoted: I'm no AR Doctor, but my Bushy did that.  Alot of others have mentioned similar things.  As someone put it to me, the bolt carrier is just making a home.

Ditto.  The point will get to a given amount of wear, and not go any further.  Don't worry about it. All of my ARs show the same wear. It occurs right at the beginning of use and then stops.  Different rifles will show a greater or lesser amount, but they almost all get some.

I would take a pic, but just describing it should do the trick. I have fired 3k out of my AR and there is no wear what-so-ever. I quess thats OK.