The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: Semi-automatics

Reply
 
Thread Tools Search this Thread
Old April 16, 2018, 03:23 PM   #1
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
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.
https://drive.google.com/file/d/1L5W...ew?usp=sharing

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

https://drive.google.com/file/d/1Lhc...ew?usp=sharing

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

https://drive.google.com/file/d/1_KI...ew?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.
NorthernBlue is offline  
Old April 16, 2018, 04:05 PM   #2
marine6680
Senior Member
 
Join Date: July 24, 2012
Location: Parker, CO
Posts: 4,489
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
Mobuck
Senior Member
 
Join Date: February 2, 2010
Posts: 6,032
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
HiBC
Senior Member
 
Join Date: November 13, 2006
Posts: 5,820
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.
HiBC is offline  
Old April 20, 2018, 12:00 AM   #5
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
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 by NorthernBlue; April 21, 2018 at 06:20 PM.
NorthernBlue is offline  
Old April 20, 2018, 06:17 PM   #6
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
Here are photos of the BCG and close ups of the cam pin itself.

https://drive.google.com/file/d/1W1i...ew?usp=sharing

https://drive.google.com/file/d/15-R...ew?usp=sharing

https://drive.google.com/file/d/1Zdw...ew?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."
NorthernBlue is offline  
Old April 21, 2018, 05:10 PM   #7
Mobuck
Senior Member
 
Join Date: February 2, 2010
Posts: 6,032
" I am thinking that is from malfunction clearance drills. "
Makes me chuckle.
Mobuck is offline  
Old April 21, 2018, 06:19 PM   #8
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
??
NorthernBlue is offline  
Old April 21, 2018, 07:23 PM   #9
marine6680
Senior Member
 
Join Date: July 24, 2012
Location: Parker, CO
Posts: 4,489
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.
marine6680 is offline  
Old April 22, 2018, 10:39 PM   #10
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
The wife just got home from using it in a 600 round carbine course this weekend. The wear didn't get any worse. :-)
NorthernBlue is offline  
Old April 23, 2018, 05:37 AM   #11
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 4,854
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.
__________________
I screw things up--so you don't have to.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old April 23, 2018, 11:03 AM   #12
Fishbed77
Senior Member
 
Join Date: November 23, 2010
Posts: 4,290
Quote:
This is a common thing in cheaper ARs.
I've seen it happen in Colts and BCMs too.

In my experience, it's a non-issue.
Fishbed77 is offline  
Old April 23, 2018, 10:42 PM   #13
marine6680
Senior Member
 
Join Date: July 24, 2012
Location: Parker, CO
Posts: 4,489
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.
marine6680 is offline  
Old April 24, 2018, 05:18 AM   #14
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
Here is a link to the img showing the "damage" to the upper.

https://drive.google.com/file/d/1Lhc...ew?usp=sharing
NorthernBlue is offline  
Old April 24, 2018, 05:27 AM   #15
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
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/1pOh...ew?usp=sharing

https://drive.google.com/file/d/1c6V...ew?usp=sharing

https://drive.google.com/file/d/1HsE...ew?usp=sharing

https://drive.google.com/file/d/1hqc...ew?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/1rG5...ew?usp=sharing

https://drive.google.com/file/d/1-kX...ew?usp=sharing

Last edited by NorthernBlue; April 24, 2018 at 05:40 AM.
NorthernBlue is offline  
Old April 24, 2018, 06:48 AM   #16
Mobuck
Senior Member
 
Join Date: February 2, 2010
Posts: 6,032
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.
Mobuck is offline  
Old April 24, 2018, 08:39 PM   #17
Duke of Lawn Chair
Member
 
Join Date: January 10, 2018
Posts: 26
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 by Duke of Lawn Chair; April 25, 2018 at 09:21 AM.
Duke of Lawn Chair is offline  
Old April 25, 2018, 05:26 AM   #18
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
I do. I just got home from work and if I remember, I will take a look tomorrow.
NorthernBlue is offline  
Old April 25, 2018, 07:04 AM   #19
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 4,854
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.
__________________
I screw things up--so you don't have to.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; April 25, 2018 at 08:46 AM.
stagpanther is offline  
Old April 25, 2018, 08:39 AM   #20
Mobuck
Senior Member
 
Join Date: February 2, 2010
Posts: 6,032
"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.
Mobuck is offline  
Old April 26, 2018, 04:02 PM   #21
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
You're right, there is a lot of lube. When going through carbine courses, I apply more lube. I don't cover everything in it but I do apply a heavier coat. It's a combo of oil and grease. When I have used just oil, it tends to either burn off or if I apply a lot it gets all over. The grease helps hold it in place and had lasted though the whole day. The dirt on the carrier is about what I expected. It's a mix of brass, carbon, lube, and dirt from the range. My 6920 looked about the same, I am personally not concerned with what I saw in that matter.

"Duty" lube, is just a light layer of oil...and with that I get more of powder residue you talk of than the goop you see in the photos.

Anyway, here are cam pin measurements that were asked for.

Colt Cam Pin Head: .4005 x .3185 x .0950 inches
Colt Cam Pin Shaft: .7115 x .3100 inches

DSArms Pin Head: .4005 x .3165 x .0955 inches
DSArms Pin Shaft: .7145 x .3090 inches

Wear Inside the Colt Upper
https://drive.google.com/file/d/1eS1...ew?usp=sharing

https://drive.google.com/file/d/1kVB...ew?usp=sharing

Colt Bolt:
https://drive.google.com/file/d/1k0m...ew?usp=sharing

https://drive.google.com/file/d/1tWg...ew?usp=sharing

DSArms Bolt:
https://drive.google.com/file/d/1XyE...ew?usp=sharing

https://drive.google.com/file/d/1Snc...ew?usp=sharing

CAM PINS:
https://drive.google.com/file/d/1aUL...ew?usp=sharing

https://drive.google.com/file/d/1J0D...ew?usp=sharing
NorthernBlue is offline  
Old April 26, 2018, 04:22 PM   #22
NorthernBlue
Member
 
Join Date: July 29, 2016
Location: Alaska
Posts: 56
And For S and Gs, The DSArm Pin weighs 7.490 Grams. The Cold Pin weights 7.454 Grams. Just had a new scale dropped at the door, so I used it. :-P

At this point in the game I am no longer concerned about the wear. I think it had everything to do with the over-gassing before I put in the H buffer and Blue Spring. Granted I have nothing to prove that at this point, other then it's no longer getting worse.
NorthernBlue is offline  
Old May 9, 2018, 06:11 AM   #23
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 4,854
In retrospect--I've seen this kind of wear pattern before--looks a lot like what happens when a carrier assembly is put back together without the firing pin (yup, been there, did that). Or maybe the cam retaining pin wasn't holding the firing pin.
__________________
I screw things up--so you don't have to.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 10:56 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2018 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.08100 seconds with 9 queries