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Posted: 3/29/2015 11:24:24 AM EDT
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Just noticed this wear when cleaning this morning. Any ideas what's causing this? This is probably after about 500rds.
Here's the specs. 11.5" barrel. Specwar 556. Carbine buffer. m16 carrier. I've never seen the cam pin cause channels like this before, esp on both sides. 
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| From what I can see in the pictures it look likes there are grooves down the side of the upper right? I know it is normal for the cam pin to carve a notch or remove material from around the half moon cut out in the upper as it drags along it during cycling because it catches the cam to move the bolt forward. But to have cuts going down both sides does not appear normal. I would suggest trying a different cam pin, it looks like yours is out of spec. Hold a new one next to yours and see if yours is wider. |
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Your upper is normal. Every upper is machined like that, it's not wear marks.
The two slots are clearance cuts for the installation and removal of your charging handle. The machined area on the left side of the upper just behind the barrel extension is cut to allow the cam pin to rotate inside the bolt carrier. Nothing to see here, move along. 
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Quoted:
Your upper is normal. Every upper is machined like that, it's not wear marks. The two slots are clearance cuts for the installation and removal of your charging handle. The machined area on the left side of the upper just behind the barrel extension is cut to allow the cam pin to rotate inside the bolt carrier. Nothing to see here, move along. Borderpatrol take a closer look at the last two pictures. There appears to be groove marks carved in the side of the upper, both sides running mostly the entire length of the upper. I think this is what the OP is asking about. |
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No. Take a second look.
Quoted:
Your upper is normal. Every upper is machined like that, it's not wear marks. The two slots are clearance cuts for the installation and removal of your charging handle. The machined area on the left side of the upper just behind the barrel extension is cut to allow the cam pin to rotate inside the bolt carrier. Nothing to see here, move along. |
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How many rounds though the upper?
The groove next to the cam pin cutout is not uncommon; much more frequently encountered, and with greater severity in some kinds of gas system configurations than in others. The linear "tracks" are where the bolt carrier rides on the inside of the receiver. Are you lubricating those contact points? Lack of lubrication, fouling, rough finish on the bolt carrier all lead to wear on those tracks. A smooth or polished appearance is common. If its through the color on the anodizing that's excessive wear. |
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Quoted:
How many rounds though the upper? Quoted:
How many rounds though the upper? Probably several thousand through the upper, but in this configuration only about 500. The groove next to the cam pin cutout is not uncommon; much more frequently encountered, and with greater severity in some kinds of gas system configurations than in others. I'm aware the groove next to the cam pin is normal, but what about the channels going back 3/4 up the upper receiver? They didn't appear until i started shooting it with the short barrel and the can. It previously had a 16" barrel and no can. The linear "tracks" are where the bolt carrier rides on the inside of the receiver. Are you lubricating those contact points? Lack of lubrication, fouling, rough finish on the bolt carrier all lead to wear on those tracks. A smooth or polished appearance is common. If its through the color on the anodizing that's excessive wear. The channels are not from the bolt carrier riding, as they are above the carrier itself. They are exactly the same height as the top of the cam pin and gas key. There are literally channels cut into the aluminum, not just finish wear. You can see pieces of the metal flaking off in the pictures. The upper is a VLTOR VIS 2A. Could excessive gas cause this type of wear? Maybe I'm just needing an adjustable gas block and heavier buffer ? |
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I think that's from the combination of the gun being a pistol upper and the can.
More gas running back through the gun and more violent unlocking hammering the bolt to unlock, and making the bolt carrier slap the upper on the left side as the cam pin hits the unlock stop on the bolt carrier. Check the cam pin. I'm pretty sure you're going to find that it's pretty beat up. Do you have an adjustable gas block on the gun? Try reducing the gas allowed. |
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