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  1. #1
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    Is this normal wear?

    My gut tells me no but I could be wrong. This is the view looking inside the ejector port.

    I tried to get some basic shots so you can see what I see.

    It seems to me that this is excessive wear but I want to get opinions from ya'll first.

    If it's not normal what could be causing it?





    What do you guys think? Is it anything to concern myself with?

    A little background... the parts are a 10.5" Ballistic Advantage barrel. CMT UPUR3 upper. A Rainier Arms Phosphate BCG and a Griffin Snach CH.

    It has somewhere near 1000 rounds through it, but probably a bit shy of that.

    The gun runs fine for the most part but I have noticed that even if I have plenty of lubrication every now an again the bolt won't go forward into full battery and I have to recharge the handle. It might happen once or twice out of a mag or it might not happen at all. From the looks of that and where it is located that the bolt cam pin is causing it.

    I will try to get some pics of the bolt up too because I have noticed some wear spots on it, but it doesn't seem like anything major, just a few wear spots where the phosphate has worn off. I am not a hard shooter but I do run this pistol/aka soon to be SBR a lot harder that I do my other gun and I put a lot more rounds through it too.

    I am thinking my issue of the bolt not going into full battery and this could be related. Maybe something is binding? Dunno.

    Please share opinions.

  2. #2
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    I just googled 'cam pin wear' and it seems like it is normal

  3. #3
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    It eventually stops once enough material is removed. It's caused by the cam pin on the forward stroke of the bolt when it picks up a round from the magazine. The resistance of the cartridge being pushed out of the magazine presses the bolt rearward, which in turn causes it to engage the cam pin in the cam slot of the carrier.
    Will - Owner of Arisaka LLC - http://www.arisakadefense.com

  4. #4
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    I can't quite tell what I'm looking at in the pictures. Is that wear just on the inside of upper receiver, on the opposite side from the ejection port?

  5. #5
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    Quote Originally Posted by Slippers View Post
    It eventually stops once enough material is removed. It's caused by the cam pin on the forward stroke of the bolt when it picks up a round from the magazine. The resistance of the cartridge being pushed out of the magazine presses the bolt rearward, which in turn causes it to engage the cam pin in the cam slot of the carrier.
    Thank you for the response. So the more I shoot it the smoother it should get then... hopefully.

    I am only seeing a few issues... but based on what you just said it makes sense... my bolt isn't all the way locking forward from time to time... I am also noticing some scoring on the body of the spent shells. Most of them have nothing but some of them have a light score lengthwise...most though have nothing. It seems to be happening because of a slightly sluggish BCG... but I could be wrong on my guess.

    As an experiment I changed the kind of lube I am using and personally I felt like I noticed a difference. I just ran a couple of mags with some plain old CLP and it seems like it is a lot smoother. I still have and use SEAL 1 but I am considering an all the way switch for the pistol/sbr... basically because it seems to require more frequent lubrication I might get a little squeeze bottle and fill it and put it in my pocket when I go to shoot. If I need a little then drop drop and back to business.

    I haven't quite decided anything for sure yet but just in a preliminary test I seemed to notice a difference.

    One thing that did happen though is when I changed lubes I was basically mag dumping and two seperate cases got jammed in the chamber... I was able to just pull them out by pulling on the CH, but the shells were unfired and bent pretty bad. Of course they were reloads so we shall see. I will keep an eye on it. I shot 90 rounds today and I will do a couple of mags every other day this coming up week to see if anything is persistent. Today was the first time ever I had bent cases...it could easily be from crappy brass though so I am not discounting that at all.

    The main thing is my bolt won't go all the way into battery sometimes. That part is the main thing that I want to solve, but it seems like all these things can and maybe are related.

  6. #6
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    Quote Originally Posted by BoilerUp View Post
    I can't quite tell what I'm looking at in the pictures. Is that wear just on the inside of upper receiver, on the opposite side from the ejection port?
    Yes. Exactly. Look straight into the ejection port and there is wear but most of it is pretty cosmetic. Right at the end though near the barrel end it is pretty worn down.

  7. #7
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    Was gonna say at first aero upper? Long inside joke thingy...lol

    But that is quite a bit from the pics, but it could be the pics though...how does the cam pin look?

  8. #8
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    The Rock River we had years ago showed even more wear then yours. Not only did the upper have a score mark on both sides of the upper bcg track, but also where the CH rode as well. For the first month or two of owning the gun you could smell the anodizing burning off when you shot the gun or pulled back the CH a few times rapidly.

    Didn't really matter which lube we used either. Eventually it stopped once the bearing surfaces became mated. The Colt 6920 did it as well but to a far lesser degree.

    In my opinion, ARs are made to a "spec", but they can be plus or minus a thousand or two. If you get a few parts all on the plus side of the spec something has to give...

    It never caused any malfunctions, just a little bit of annoyance.

  9. #9
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    use it till it breaks and then buy something higher quality..

  10. #10
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    IMO, no, this is not normal, but it is not unheard of either. I think the typical wear pattern is around the 5 and 7 o'clock positions (if looking head on at the bcg) as that is where the upper supports the weight of the BCG. As an experiment, I'd blacken the worn area and run a different BCG for a while to see if it wears the same way. That will tell you if it is the upper that is slightly out of spec or the BCG. You can of course continue to run what you have and it will eventually wear itself in, but make sure you install the cam pin the same way every time.

    POF has a product that may help, too, if you want to throw money at the problem: https://www.rainierarms.com/pof-223-roller-cam-pin

    I'd probably be tempted to go in and smooth and polish out the worn area of the upper and be done with it.
    Last edited by BoilerUp; 28 February 2016 at 10:02.

  11. #11
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    Quote Originally Posted by voodoo_man View Post
    use it till it breaks and then buy something higher quality..
    Which component/manufacturer do you suggest is of insufficiently hight quality? The CMT upper or the RA BCG? Both RA and CMT have pretty good reputations for quality.

  12. #12
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    Quote Originally Posted by BoilerUp View Post
    Which component/manufacturer do you suggest is of insufficiently hight quality? The CMT upper or the RA BCG? Both RA and CMT have pretty good reputations for quality.
    Never said they were of low or insufficient quality. But if its having an issue then there is obviously an issue.

  13. #13
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    What kind of mags are you running?
    Premium AR-15 parts for the customer who demands reliability and quality.
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  14. #14
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    Quote Originally Posted by Fathom_Arms View Post
    What kind of mags are you running?
    Magpul PMags. I have 20 and 30 rounders. Both are pretty new still.

  15. #15
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    More than likely its tolerance stacking between the cam pin and upper. Cam pin may be out of spec. try swapping it out with a different one. Sounds like its dragging enough to slow the bcg down and prevent it from going into battery. Run your guns wet. Lubrication is a significant factor on the coefficients of friction for phosphate coatings.
    Last edited by Stone; 28 February 2016 at 17:16.
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