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Thread: short stroking CAR upper? any advice?

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    Gunco Addicted for life j427x's Avatar
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    Postak short stroking CAR upper? any advice?

    one of my pals brought in a new CAR 16inch upper for me to try to get running.

    from what he had told me it will fire a round--eject the spent case and then go click on an empty chamber.

    i took it out to my pasture/range today and sure enough. you can charge up a round fire it and it ejects the spent case very nicely. and it does the same thing over and over. fires the hand charged round,ejects the spent case but then fails to load another round in the tube--they you get "click"-

    changed ammo , mags and used some of my pmags= the same shit. cleaned it up and lubed it up. same shit. checked the ring gap and the key--they look good to go.

    sprayed some solvent down the gas tube and it went gushing out the port in the barrel so the port is clear. the front sight don't look canted?

    i haven't tried the one-shot mag bolt hold open trick yet--should have done that while i was out today. but it was like 103f. i also haven't swapped bolts or BC&gs yet.

    it acts like it is short stroking tossing the spent case out but not going back enough to charge in a fresh round? any ideas? cures?

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    No Hope For Me Coils's Avatar
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    it acts like it is short stroking tossing the spent case out but not going back enough to charge in a fresh round? any ideas? cures?
    The only thing I've seen like this was a short stroke, new Bush Master would fire a round then it either wouldn't feed or it would jam when feeding the next round. The cure was a softer recoil spring, rifle still works fine.
    Don't know if this would help in your situation.

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    Gunco Good ole boy tanvil's Avatar
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    Quote Originally Posted by Coils View Post
    The only thing I've seen like this was a short stroke, new Bush Master would fire a round then it either wouldn't feed or it would jam when feeding the next round. The cure was a softer recoil spring, rifle still works fine.
    Don't know if this would help in your situation.
    Plus if he just finished putting it together, check and make sure the gas tube and gas key are lining up properly.

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    Gunco Veteran [486]'s Avatar
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    CARs are very ammo sensitive from what I hear, try something heavier duty for the first few hundred, wear the parts in a bit. Maybe heavier bullets.

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    Gunco Regular resting's Avatar
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    They are ammo sensitive. Some don't like Wolf ammo and short stroke frequently when trying to use it.

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    Gunco Addicted for life j427x's Avatar
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    as far as ammo it is doing this on all the ammo i have tried so far.

    i haven't tried my black hills 77grainSMKs yet but i will today. i am going to switch BCG's and use one of my LMT units. too.

    if these tricks don't get it to cycle i think a tear down may be required. maybe a gas tube change?

    i wouldn't think it is the recoil spring as i tried the upper on a couple fully functional lowers with the same results on the FTF issue.

    this one is a real hair puller!!

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    gunco irregular moleman's Avatar
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    I bought a M&A parts 11.5" with perm attached 5.5" flash hider car upper back in the late 80's early 90's that started off not extracting, then when I got that fixed it was short stroking. I couldn't find anything wrong with it either. I know its considered blasphemous, but I drilled out the gas port slightly larger and it ran fine for about 10 years until I got rid of it. I was lucky because where I worked at the time had just about all drill bit sizes fractional, number, letter, and metric which allowed me to find one that was only a couple thousands larger. I drilled it, test fired it and ended up drilling it with the next size bit up for good measure. The total I enlarged it was only about .003"-.004" which was enough to solve the problem. I had a eagle arms upper that had a burr at the gas port hole on the inside of the barrel. It ended up getting blown down the gas tube and wrecking the gas rings the first trip out. Maybe he had a burr in there too that is partially obstructing the gas system.

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    Gunco Addicted for life j427x's Avatar
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    last one i had doing shit like this was an LMT 14.5 upper i bought from a friend that i knew was having some problems. what it had was a metal shaving in the gas port. it would cycle evry so often then jam or not load a round. this one is not feeding a new round--ever.

    i am thinking it is either something in the gas port/tube/gas system or the port hole might be a tad too small or maybe the FSB /gas tube-might be a tad offset.

    BTW-this is a del ton upper which he has voided the red-tag warr by firing wolf in it right off the bat. i try to do every trick in the book before i take the front sight base off as it is a PITA!! i'll get it ironed out one way or the other. and my other del-tons seem to run wolf fine --go figure--lol

    test fired it with the 77g ammo and LMT bolt carrier. it will feed some then either jam or skip loading a new round. it even cycled a couple 55gr rounds normal for the first time. it is about at 55% it is wanting to run but something is off about this upper.

    i am going to pull the gas tube, and if i can't see anything wrong then the FS-base has to go as much as i dread pulling it--






    Quote Originally Posted by moleman View Post
    I bought a M&A parts 11.5" with perm attached 5.5" flash hider car upper back in the late 80's early 90's that started off not extracting, then when I got that fixed it was short stroking. I couldn't find anything wrong with it either. I know its considered blasphemous, but I drilled out the gas port slightly larger and it ran fine for about 10 years until I got rid of it. I was lucky because where I worked at the time had just about all drill bit sizes fractional, number, letter, and metric which allowed me to find one that was only a couple thousands larger. I drilled it, test fired it and ended up drilling it with the next size bit up for good measure. The total I enlarged it was only about .003"-.004" which was enough to solve the problem. I had a eagle arms upper that had a burr at the gas port hole on the inside of the barrel. It ended up getting blown down the gas tube and wrecking the gas rings the first trip out. Maybe he had a burr in there too that is partially obstructing the gas system.
    Last edited by j427x; 06-25-2009 at 01:07 PM. Reason: update

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    Gunco Addicted for life j427x's Avatar
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    update to the update.

    i have tried every trick i know to get this one up and running and no-dice.

    looks like i am going to pull the front sight base and possibly enlarge the gas port if i don't find anything that might be blocking the port hole.

  10. #10
    GunLegume lim144's Avatar
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    So this happened to me 10 years ago on my CAR that parts came from everywhere but most of upper was from Model-1. I found it to be a gas problem by measuring the spring weight on the operating handle. I put a tape on the operating handle and hooked a scale, fishing scale, on it and pulled it all the way back. It mapped pretty close to the other rifle that wasn't having a problem. So I knew it wasn't the bolt, plunger, spring nor the pin...

    So I pulled the gas-tube out. Inspected it. Got frustrated to find nothing. Put the damn thing together, took it to my friend's farm to have him look at the problem, and the stupid thing shot just fine. "What problem?", my smart ass friend replied after shooting few different ammo through it.

    Feel your pain. The process took 2 months to work itself out. I have no idea what the reason was, but I'm sure someone here is smart enough to resolve this.

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