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Old April 16, 2018, 03:23 PM   #1
Join Date: July 29, 2016
Location: Alaska
Posts: 48
AR-15 Cam Pin Wear On Upper?

I have 3 AR-15s. One is a Ruger AR556. One is a Colt LE6920. The other is a Ruger AR556 Lower with an Anderson upper and a DSARMs BCG. The Ruger AR556, with Ruger Upper and BCG shows no wear from the cam pin. There is about 2000 rounds though that rifle. The LE6920 has about 2000 rounds through it. It has some wear on the upper from the cam pin. The Anderson upper with DSARMs BCG has the most wear. It has about 500 rounds on it. It does not seem to be affecting its function. This rifle has had no malfunctions except for magazine related ones. The Anderson build has a B.A. 14.7 Mid-length barrel on it. It was overgassed for about 300 rounds. I put in a heavy buffer with Blue Springco which helped tame down the kick alot. I am wondering if the fast and rough cycling is what caused the wear? Any thoughts? I included photos of the Ruger showing no wear and the Anderson showing the wear.

The Ruger and Anderson.

Close Up of The Anderson.

Close Up of The Ruger.

The LE6920 isn't kept in the house, so I am being lazy and not including photos of it, but it about halfway between wear wise.
NorthernBlue is offline  
Old April 16, 2018, 04:05 PM   #2
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Join Date: July 24, 2012
Location: Parker, CO
Posts: 4,304
It happens in some uppers.

It may be related to an issue, like gassing or timing... Maybe a BCG that isn't in spec.

Generally it is self limiting.
marine6680 is offline  
Old April 16, 2018, 10:15 PM   #3
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Join Date: February 2, 2010
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Not something I'm going to spend much time worrying about. I guess I could go down and pull a bunch of bolts to see if or how much this is happening on my AR's but I haven't really noticed any problems.
Mobuck is offline  
Old April 17, 2018, 09:51 PM   #4
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Join Date: November 13, 2006
Posts: 5,635
I'm just not seeing something,I guess.
The pix show ejection port and some BCG.
Wait,OK. I see the wear in question.

I don't like to see the hard anodize wear through.

I wonder if they all have the same quality of anodizing.

When the BCG is assembled,is the cam pin above or below flush with the BCG?

If its standing high,,HMMM,why is that? One little observation from manufacturing is corner conditions in assemblies. Consider the outside corner,such as you would find on the edges of a cube,versus the inside corner you would find in a milled pocket.

A sharp outside corner is easy,machining often produces them.A sharp inside corner isharder to do,and generally a bad idea (stress riser)
A sharp outside corner may prevent proper assembly with a less sharp inside corner.
Just a little attention (chamfer) to an interfering sharp edge may fix it.

I see a scratchy surface. What are the "claws" that are scratching?

Your cam pin may have some little micro-dinks on the edges .The dinks deform the steel and make high spots. A few strokes with a fine stone cleaning edge conditions might solve it.

Lower cost parts may not see all the operations a higher cost sees.
Individally hand deburring and chamfering each cam pin will not happen in production.Maybe ,they spend time in a vibratory bowl with ceramic media.But I can see and fix this stuff.

We can look at each part,feel the edges with a thumbnail or a pencil,look with a loupe,and give them a minimal touch up with a little hard India stone.

You might even get radical and rub the head of the cam pin 8 or 10 strokes on a sheat of 600 wet or dry.
Good luck.

Last edited by HiBC; April 17, 2018 at 10:40 PM.
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Old Yesterday, 12:00 AM   #5
Join Date: July 29, 2016
Location: Alaska
Posts: 48
All the rifles have the same wear with the anodizing in the slot where the charging handle rides. I am thinking that is from malfunction clearance drills. Running the drills puts a lot of sideway pressure on the changing handel. The scratch marks are from dirt and what not caught up in there.

I am mostly trying to figure out what is with the "digging" near the rear of the semi-circle cutout on the receiver.
NorthernBlue is offline  
Old Yesterday, 06:17 PM   #6
Join Date: July 29, 2016
Location: Alaska
Posts: 48
Here are photos of the BCG and close ups of the cam pin itself.

DSArms (The BCG manufacturer) reviewed the post and sent the following...
"1- The cam pin itself may have a slight bur on it that may have caused the issue.

2- The receiver may not be correct in terms of the where the radius starts to allow the pin to rotate. If this is the case it may be the receiver is in the way when the pin goes to start its rotation.

3- Based on his own observations; the gun started out over gassed. This issue can lead to the gun beating itself up, the cam pin doesn't not have time to properly rotate in and out of position during the increased cycle speed due to the gun being over gassed."
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