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Thread: Ground Bolt and Rollers...

  1. #1
    Senior Veteran MicroPilot's Avatar
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    Ground Bolt and Rollers...

    Heres what I have:

    CAI Stamped CETME with a bolt measuring 1.824" and rollers with a diameter of .312" (7.94mm).

    Bolt gap measures >.028" and there is no gap at the cocking handle.

    Will replacing the bolt and rollers be the best route to getting this gun back in specs?
    Last edited by MicroPilot; 03-25-2007 at 02:11 PM. Reason: typo

  2. #2
    Ol'30 Grit jfowl31's Avatar
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    well.... those rollers are small for one. 8.0 mm are standard, 8.02 are +2, and 8.04 are + 4

    I dont know what you have there.

    if you r gap is .028, and your bolt length is 1.824, it means that your bolt is .011 too short (nominal is 1.835), so your true gap is .017, so to answer your question... replacing the ground bolt head and rollers SHOULD get everything current and into spec.

    Sometimes the rifles can do funny things when you replace parts, but typically, they dont.

    Id say buy a new bolt head, and some standard and +2 and +4 rollers and see what combo gives you the best combination of perfect operation and low recoil.

    And maybe remeasure those rollers to see if we can confirm the they are in fact "-6's" as you posted above.
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  3. #3
    Senior Veteran MicroPilot's Avatar
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    I double checked the rollers and they are 7.94mm

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    Senior Veteran SSwee's Avatar
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    No gap at the cocking handle is going to throw everything off. I've been through that with mine having a ground carrier from CAI and putting a non ground carrier in it's place trying to get a better bolt gap. If he has a bolt gap of .017" but is hitting the cocking handle the bolt gap may actually be quite a bit less. It would not be easy but may be necessary to pull the cocking handle and piston to check the bolt gap accurately. It will also give a more accurate measurement on the interference with the cocking handle.
    SS
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    Veteran bullseye's Avatar
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    Quote Originally Posted by MicroPilot View Post
    I double checked the rollers and they are 7.94mm
    Contact Big Steve about your rollers, sounds like they are undersized and he might have use of them.
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    Ol'30 Grit jfowl31's Avatar
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    I didn't see the no cocking tube gap... that needs to be addressed first so you can get an accurate bolt gap measurement.

    Even if that measurement is right, and they ARE in fact 7.94 mm... Ive nver heard of rollers that size. -6's are not something Ive ever seen for sale, for any of the Hk series of rifles, though Im sure Perro or M1 will chime in here in a second to enlighten us on what -6's are used for.

    So should he just grind the carrier to get some cocking tube gap like Century did? or is there a bter fix that doesnt involve cutting it off and resetting it?
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    Senior Veteran MicroPilot's Avatar
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    OK,

    With the cocking handle assembly removed my bolt gap goes down to .009". Does this mean I just need to remove .020" from the end of the carrier tube? If it would be better to buy a new bolt and rollers, I'm not opposed to doing that instead.
    Last edited by MicroPilot; 03-25-2007 at 10:33 PM.

  8. #8
    Senior Veteran SSwee's Avatar
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    Is that .009" after subtracting the .010" or .011" for the ground bolt head?
    If it's not then your down to no bolt gap. +4 rollers will help but I don't see it fixing your problem. With the .028"+ you were getting before, you have about .020" interference on the cocking tube. If you can get the bolt gap right, the cocking handle gap should be OK. Gear shanty has a bolt carrier assembly for $28.00. He's a righteous guy to deal with. That would be where I would start. There is a chance that you could replace the bolt carrier assembly and still have no bolt gap. In which you may be down to repressing the barrel. If I'm off base let someone speak up.
    SS

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  9. #9
    Senior Veteran MicroPilot's Avatar
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    No, I did not account for missing length of the ground bolt.

    I will order a bolt assembly tomorrow. Should I get extra rollers also?

    Did Century remove material from the front or rear of the bolt?

  10. #10
    Senior Veteran SSwee's Avatar
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    They grind off the back of the bolt head.
    I get +rollers from RTG. It don't hurt to have on hand but wether they will be needed will depend on the effect of replacing the bolt carrier assembly. If it gives you a bolt gap of .005" or .006" then the + rollers should be a benefit. If there isn't a bolt gap with the different bolt carrier assembly then the + rollers won't be of much use. My CAI sporter is at .006" bolt gap. It shoots good now but if it looses any more gap I'll be pressing the barrel.
    SS
    Last edited by SSwee; 03-26-2007 at 12:01 AM.
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