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Thread: bolt doesn't fit on ak74 build

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    Gunco Rookie go_home_red's Avatar
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    Default bolt doesn't fit on ak74 build

    I'm about to install the barrel on my ak74 build. At least, I think I am. But I am running into a problem with the bolt not fitting in the receiver.

    http://s154.photobucket.com/user/go_...tml?state=copy

    (couldn't get the image to load, so copy and paste the link above)

    Does it look like I welded the rails too high? The bolt hits the upper lip on both sides of the receiver when it sits on the rails.

    Any insight into what I'm doing wrong would be appreciated, as would any recommendations of where to go from here. Thanks!
    Tommo likes this.

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    GuncoHolic 00redZX-6R's Avatar
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    I guess I have never tried to put just the firing pin part of the bolt in. I always put the firing part into the the other part of the bolt with the piston and charging handle attached. Can't think of the actual names of the parts right now. I think the firing pin part you have sits lower than the other part of the bolt. I could be way off, but I would put the two parts together and try it.

    You might need to do some altering, but that is one you figured out hte issue.

    The reeiver is crushed together at all is it?

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    Gunco Rookie wylie442's Avatar
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    Your analysis sounds right.

    Based on what you're describing I could see either the lower rails being welded in to high (they should line up perfectly to the trunnion and be parallel to the top rails) or the rails being welded in with a slight upward slope (not parallel to the top rails) from the trunnion.

    If it is the later and it's not off by too much you might be able to massage the rails down with a punch but it could get ugly. I've done that for some minor fitment issues. If the rails are plain old too high I'd try to pop them off and reweld.

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    Gunco Rookie go_home_red's Avatar
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    The receiver is not crushed or bent--the front and rear trunnions and the center support are riveted in, so everything should be the correct width. I do need to file down the upper edges of the receiver so that the bolt carrier will slide easily (it is very, very tight right now), but I would think that to be an indication that the receiver is--in terms of width--where it should be.

    Placing the bolt into the bolt carrier does not solve the issue. When I install the bolt in the bolt carrier and attempt to install the set into the receiver, the bolt still runs into the upper lip on the receiver. This is what makes me think that I installed the rails too high. See the following photos, as the rails don't line up with the front trunnion quite as well as I thought they did:

    Right rail
    Left rail

    I'm all ears, but I'm guessing I'm out a receiver and that I should be more careful next time I weld the rails. :-( Would love to be wrong!

    Edit: The lower rails are parallel to the top rails on the receiver. No luck there...although I would think the solution would be the same :-(

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    Chief Administrator 7.62x39's Avatar
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    From the pics it does look like the rails are too high. Do you have a pair of vernier calipers? What is the measurement between the rails?
    .

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    Gunco Regular Ken3030's Avatar
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    From what I can tell on the pics your rails are too high and something is wrong if your bolt carrier is very, very tight. Maybe you got the wrong center support in there. I usually have to tweak the rails a bit but it shouldn't be that tight.
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    Gunco Regular allesennogwat's Avatar
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    The space between the tops of the lower bolt rails and the bottoms of the stepped upper bolt rails on an AK-74 should be a minimum of 6.0 mm to a maximum of 6.3 mm.

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    Gunco Rookie go_home_red's Avatar
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    Quote Originally Posted by 7.62x39 View Post
    From the pics it does look like the rails are too high. Do you have a pair of vernier calipers? What is the measurement between the rails?
    I do have a set of calipers, but I can't get them into the receiver without interference. I used a 15/64 bit to set the "height" of both of the rails.

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    Gunco Rookie go_home_red's Avatar
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    Quote Originally Posted by allesennogwat View Post
    The space between the tops of the lower bolt rails and the bottoms of the stepped upper bolt rails on an AK-74 should be a minimum of 6.0 mm to a maximum of 6.3 mm.
    That sounds like the issue with the rails--a 15/64" bit would be 5.95 mm. I'll keep your info in mind next time. Thanks for that.

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    Gunco Rookie go_home_red's Avatar
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    Quote Originally Posted by Ken3030 View Post
    From what I can tell on the pics your rails are too high and something is wrong if your bolt carrier is very, very tight. Maybe you got the wrong center support in there. I usually have to tweak the rails a bit but it shouldn't be that tight.
    I'm guessing my receiver was a bit rough (needed filing). The top rails (the rails on the receiver itself) were not even when I got the receiver--the right side is 0.232", the left is 0.204". The center support was from AK-Builder.com, as were the rails. The receiver was from keepshooting.com

    Thanks for all of the replies. I guess I'm not too bothered by the loss of this receiver, as I didn't like how the rail welds turned out (I had a 240 volt Harbor Freight spot welder, so that's what I used...the welds were not pretty, even with the AK-Builder tips) and I had to work on the front trunnion holes more than I would have preferred. The next one will go together better.

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