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Thread: Carrier shift during dry-firing (and I'm assuming live fire also)

  1. #11
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    Quote Originally Posted by Iraqgunz View Post
    Strip the carrier down and then take your upper receiver and flip it upside down. Visually look at the tube to see if it is straight. Then insert the carrier into the upper and slowly ride it forward. If it is binding or hesitating then it is hitting the carrier key and needs to be tweaked.
    I rode the carrier forward slowly with my pinky with and without the bolt and I felt no binding. I looked over the gas key and the gas tube to see if there is any marring on it and it all looks good (although the rifle does only have about 200 rounds through it).

    I don't have any specialty tools, but I applied a bunch of paste lubricant to the upper receiver to see if the gas key is riding in straight and it looks dead center in the upper receiver, same with the gas tube.

    What else could it be? Out of spec upper? It's an Aero Precision.

  2. #12
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    I think you are probably worrying about nothing. I would just keep shooting.



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  3. #13
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    Could just be the firing pin making contact with the bolt tail as the hammer strikes it,forcing the bolt foward in the barrel extension ever so slightly and coming to rest on the barrel breech face,the cam pin shifting in its jounal of the carrier as the bolt is impacted.

    Also remember that the only thing keeping the carrier centered and running true without rotation is the gas key,as it rides in the channel of the upper.There is a slight tolerance to allow smooth function,so it could just be the above,or the carrier just centering itself under impact.

    Like IG said,worrying about nothing, if all critical reas check out.
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  4. #14
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    Is this something that would affect accuracy? I don't expect this to mickey mouse at 400 yards, but I was hoping for at least a MOA.

  5. #15
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    Are you having malfunctions when firing? If you have followed IGs advise and found no issues. I'd just shoot it as is some non-standard stuff has to wear in. Not normally in ARs but this one is for precision / target shooting.. it's more likely to be tolerance stacking issue. Check for wear in / marks after cycling it. I normally go through 500 + rnds before depending on a firearm some even more. IMHO My $.02
    Last edited by blade_68; 09-16-13 at 12:48.
    NRA Life Member.

  6. #16
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    Quote Originally Posted by netchemica View Post
    Is this something that would affect accuracy? I don't expect this to mickey mouse at 400 yards, but I was hoping for at least a MOA.
    Unless the bolt is moving, and from what you've said I've heard of no indication of that, then this should have no impact upon accuracy.

    I tried swapping one carrier out in two different uppers and was able to get the carrier to move slightly (less than a mm) in both with the bolt locked into battery. However, the bolt did not move. Nothing to worry about, IMO.

  7. #17
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    There's a reason you test for gas key alignment with your receiver upside down. When you are actually shooting your rifle, you'll have a magazine inserted, which puts upward pressure on the bolt carrier.

    You shouldn't be surprised that the bolt carrier moves a little when the hammer slams into the firing pin, which in turn transfers force into the bolt carrier, especially when there's no magazine inserted.

    Also, keep in mind that when you're actually firing the rifle, the chamber pressure is high enough that the bolt is friction locked in the barrel extension. The bolt is not going to rotate and unlock until the bullet has left the barrel, assuming everything is operating correctly.

    Your worry about slight carrier movement while dry firing hurting accuracy is overblown when you consider that the entire bolt carrier group and buffer are slamming back and forth every shot.

    And if it still really bugs you that the carrier moves a teeny bit, try it with an empty magazine inserted.



    Edit:

    I also couldn't help but notice that you're using button head philips screws that are too long in your CMR rail in the video. The correct replacement screws can be found at McMaster, 7/8" black oxide alloy steel flat head socket cap screw, part number 91253A198. Try this direct link, or just search for the part number on their site: http://www.mcmaster.com/#91253a198/=oj94yw.

    They also sell special high-torque allen keys that won't strip out the socket cap as easily, for only 26 cents apiece. Part # 71285A152 or link: http://www.mcmaster.com/#71285a152/=oj960c

    You definitely should not be using a button cap screw on the CMR, because you're only contacting the outer rim, which is putting undue stress on the fastener and also can damage the rail. You also want to use alloy steel for strength over stainless, and the black oxide coating reduces the chance of rust.
    Last edited by Slippers; 09-16-13 at 13:38.

  8. #18
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    Quote Originally Posted by Slippers View Post
    There's a reason you test for gas key alignment with your receiver upside down. When you are actually shooting your rifle, you'll have a magazine inserted, which puts upward pressure on the bolt carrier.

    You shouldn't be surprised that the bolt carrier moves a little when the hammer slams into the firing pin, which in turn transfers force into the bolt carrier, especially when there's no magazine inserted.

    Also, keep in mind that when you're actually firing the rifle, the chamber pressure is high enough that the bolt is friction locked in the barrel extension. The bolt is not going to rotate and unlock until the bullet has left the barrel, assuming everything is operating correctly.

    Your worry about slight carrier movement while dry firing hurting accuracy is overblown when you consider that the entire bolt carrier group and buffer are slamming back and forth every shot.

    And if it still really bugs you that the carrier moves a teeny bit, try it with an empty magazine inserted.



    Edit:

    I also couldn't help but notice that you're using button head philips screws that are too long in your CMR rail in the video. The correct replacement screws can be found at McMaster, 7/8" black oxide alloy steel flat head socket cap screw, part number 91253A198. Try this direct link, or just search for the part number on their site: http://www.mcmaster.com/#91253a198/=oj94yw.

    They also sell special high-torque allen keys that won't strip out the socket cap as easily, for only 26 cents apiece. Part # 71285A152 or link: http://www.mcmaster.com/#71285a152/=oj960c

    You definitely should not be using a button cap screw on the CMR, because you're only contacting the outer rim, which is putting undue stress on the fastener and also can damage the rail. You also want to use alloy steel for strength over stainless, and the black oxide coating reduces the chance of rust.
    You have no idea how much I appreciate that edit. I have been looking everywhere for replacement screws after I stripped out the originals. I ended up settling for some home depot garbage due to lack of results. I'll place an order for the right screws when I get home.

    Again, thank you!
    Last edited by netchemica; 09-17-13 at 13:08.

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