AR-15 Cam Pin Wear On Upper?

N

NorthernBlue

New member
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.
https://drive.google.com/file/d/1L5WjK3MIsbIzX0nGxWZv7Pp9olgZ3Rb1/view?usp=sharing

Close Up of The Anderson.
https://drive.google.com/file/d/12uyf7wQHiZOIzX3vrWc58nbtOy9FB4ck/view?usp=sharing

https://drive.google.com/file/d/1LhcYNCus3PKvCjSb7TgqarSlhUGS5uL-/view?usp=sharing

Close Up of The Ruger.
https://drive.google.com/file/d/1yKEHp_EUKh6RbOdIADuFqma9Lonezeb9/view?usp=sharing

https://drive.google.com/file/d/1_KIyPzw8gnMSLsJdaqclStEcvUPkrFTb/view?usp=sharing

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.
 
M

marine6680

New member
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.
 
M

Mobuck

Moderator
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.
 
H

HiBC

New member
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:
N

NorthernBlue

New member
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 sideways pressure on the changing handle. 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.
 
Last edited:
N

NorthernBlue

New member
Here are photos of the BCG and close ups of the cam pin itself.

https://drive.google.com/file/d/1W1iQ92d8A5Thnmzks1ua8dvg-w8VHTdK/view?usp=sharing

https://drive.google.com/file/d/15-R8gt3Enhr_zFmrT74_bcLl8ZaWBumq/view?usp=sharing

https://drive.google.com/file/d/1ZdwsuZa8McdSbJWUOowDNqPd3L3eZ8Bw/view?usp=sharing

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."​
 
M

marine6680

New member
Just keep an eye on it...

It shouldn't get much worse.

This is a common thing in cheaper ARs. I have heard about such wear for a while, in various forum posts, and it usually stops getting worse at some point.
 
S

stagpanther

New member
You never showed any pictures of the wear to the receiver by the cam pin--can you post pics of that? I've seen a few bolts and cam pins that were a bit "loosey goosey"--meaning the bolt OD to carrier ID was a bit much, allowing the pin to move around a bit much. Coated BCG's and receivers seem to be especially prone to "micro out of aligment" issues in my experience.
 
M

marine6680

New member
Yeah, but I believe it is less common on the better built rifles like Colt, BCM, and others.

Ultimately it's not really an issue, but I have seen some really bad ones in a few posts.
 
N

NorthernBlue

New member
Here are photos of it dirty after it came home from the carbine course. You should be able to zoom in pretty far on all these photos.

https://drive.google.com/file/d/1pOhaUkPNcgZEOfXEhSF0yKPGeVmGT3Ho/view?usp=sharing

https://drive.google.com/file/d/1c6Vp9hWY7WjuOyZl6_0Xe_xVPhRGoy-J/view?usp=sharing

https://drive.google.com/file/d/1HsERwYpJ5vG1uf2h582NZLxFvjSyM3Cu/view?usp=sharing

https://drive.google.com/file/d/1hqc1Eb2LuntXl2z1P2nX8qPXXWwJ9cly/view?usp=sharing
(I wiped the BCG down, it wasn't this clean or dry)

I would also like to note that Anderson is offering to take the upper back and exchange it for a new one. I am not entirely sure I want to bother to be honest. It seems like the wear has stopped.


For good measure and everyone likes photos. I took two more photos of the wear as it sits now.

https://drive.google.com/file/d/1rG5NFZCWTRz2cTN7cqFWkLiTPp3Ey9j4/view?usp=sharing

https://drive.google.com/file/d/1-kXgAfmOt51hvzrNADS9VsVVpSc77_bl/view?usp=sharing
 
Last edited:
M

Mobuck

Moderator
I'll have to say that most of the cam pins I've seen/used aren't squared off like one in your pics. Most likely it's as simple as incompatibility of that particular pin. I really couldn't see any glaring "wear points" but the thing is too filthy to see much of anything.
 
D

Duke of Lawn Chair

New member
If you have a set of dial calipers it would be interesting to see some of the dimensions of the cam pin.

@ Mobuck; Post #14 picture, just to the left of the pin head cut out.
 
Last edited:
S

stagpanther

New member
From your first cleaned picture I see clear signs of an impact on the cut-out--that is abnormal. Your dirty carrier pictures look pretty strange too--almost looks as if unburnt powder is mixed in. Did you check all your spent cases? My personal opinion is that burning off lots of rounds fast is not a great idea until you really understand what's going on--taking a net vote is not what I would say is a great idea. Because you have assembled the gun from different manufacturers you need to see what's going on with the entire weapon assembled IMO. Looks to me like you may be "over-lathering" your lubrication judging from the molten look over your residue--I usually get caked-on deposits but never go hundreds of rounds between cleaning so maybe this is normal, I don't know for sure, but over-lubrication can cause a gun to blow up.

Perhaps you also had one ignition with a cartridge that was slightly out of battery.
 
Last edited:
M

Mobuck

Moderator
"Mobuck; Post #14 picture, just to the left of the pin head cut out."

Now I see it. That's definitely caused by the squared off corner on the cam pin. May be some issue with the firing pin hole allowing the pin to rotate or simply insufficient clearance for that big, square head or the bolt carrier is torquing inside the upper more than it should.
 
You must log in or register to reply here.
Top