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Thread: Reliability problem with AC556F

  1. #21
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    Quote Originally Posted by MegademiC View Post
    Action hesitated how?
    While shooting?
    While manually cycling?
    Bolt traveling rearward or forward (if you could tell)?
    While shooting. It's hesitating when cycling on full auto. There's no way to know whether it's happening when the action is going forward or rearward.

    I swapped the bolt components back to their original rifles and then swapped the stocks and trigger packs. Two weeks ago I shot them again. The older AC556F ran 100% with the stock and trigger pack from the new rifle installed. The newer AC556F had multiple failures to extract fully, spent cases caught when the action when back forward and several hesitations while cycling. Conclusion, the stock and trigger pack are not the issue.

    Yesterday, I swapped the stocks and trigger packs back to the original rifles. I then cleaned the chambers and checked the headspace of each rifle using my 5.56x45 headspace gauges. Neither rifle would close on a Go gauge. I then swapped bolts between the rifles. Again, neither would close on a Go gauge. During the process, I used my Hornady headspace comparator tool to take some measurements and found the following:
    Manson 5.56x45 Go Gauge: 3.461"
    Manson 5.56x45 NoGo Gauge: 3.467"
    Fiocchi 223Rem 55gr FMJ cartridge: 3.456" to 3.457"
    Spent Fiocchi 223Rem case from old AC556F: 3.457"
    Spent Fiocchi 223Rem case from new AC556F: 3.460"
    Norma 223Rem 55gr FMJ cartridge: 3.467" to 3.468"
    Spent Fiocchi 223Rem case from old AC556F with the new AC556F's bolt: 3.462" (measured after shooting the same day)
    Spent Fiocchi 223Rem case from new AC556F with the old AC556F's bolt: 3.459 to 3.460" (measured after shooting the same day)

    Based on the fact that neither rifle would close on a Go and the spent case measurements are all less than the Go measurement, it seems to me that both have tight headspace.

    Here's what happened when I fired each rifle.
    New AC556F with the old AC556F's bolt:
    1x30 Fiocchi 55gr FMJ: 1 failure to completely extract the cartridge.
    1x20 Fiocchi 55gr FMJ: 100%
    1x25 Fiocchi 55gr FMJ: 100%
    1x30 IMI M193 55gr FMJ: 100%
    1x20 Norma 55gr FMJ: 100%

    Old AC556F with the new AC556F's bolt:
    1x30 Fiocchi 55gr FMJ: 1 hesitation during cycling.
    1x20 Fiocchi 55gr FMJ: 100%
    1x25 Fiocchi 55gr FMJ: 1 hesitation during cycling.
    1x30 IMI M193 55gr FMJ: 100%
    1x20 Norma 55gr FMJ: 1 failure to eject where the spent case got caught by the action going forward.

    So this is the first time that I was able to make the old AC556F have any sort of reliability issue. The only thing that was different was the bolt being swapped between the two rifles. I really don't know what to conclude here. It seems that swapping the bolt definitely caused the old reliable AC556F to have issues, so that would lead me to believe that the bolt in the new AC556F is the problem. However, there was that failure to completely extract the cartridge when shooting the first magazine through the new AC556F with the old AC556F's bolt.

  2. #22
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    I know this is going to sound silly but do you have any 62gr ammo?

  3. #23
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    Yes. However, this rifle was manufactured when 55gr was the thing and it's failing with multiple factory loads. Plus, I'm trying to keep the variables down.

  4. #24
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    Quote Originally Posted by Bret View Post
    Yes. However, this rifle was manufactured when 55gr was the thing and it's failing with multiple factory loads. Plus, I'm trying to keep the variables down.
    Fair enough.

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