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Thread: tight chamber test using a live cartridge.

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    tight chamber test using a live cartridge.

    the idea is to disassemble the rifle, drop a live round in the chamber, push it in with a finger, and then turn the muzzle up and see if the round falls out.

    Is this "test" valid? Or just more internet BS?

    For what it's worth, I did this to my cmmg upper.

    The round would not fall out but one downward shake/jolt or bump to the back of the receiver would release the round. The chamber didn't seem tight at all.

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    I would think just based on the fact that most of the measurements in the AR chamber are down to a thousandth of an inch, that this test will in no way indicate if you have a tight chamber or not. My thought is that you will get the same results with both kinds of chambers regardless of the ammunition used. What those results will be I couldn't tell you, but my hypothesis is that simply due to surface tension it will take some sort of violent action to remove the round from the chamber, whether that chamber is .223 or 5.56.
    Last edited by Mac5.56; 11-19-10 at 01:10.
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    I would think just based on the fact that most of the measurements in the AR chamber are down to a thousandth of an inch, that this test will in no way indicate if you have a tight chamber or not.
    I don't see why not.

    Unless the 5.56mm nato chamber allows for a round to wiggle in the chamber and not stay put, I can't see how a barrel (in my case) would be considered "tight".

    I did the same to my wasr and the 7.62x39mm live round was literally wiggling in the chamber and would not stick at all. But when I put a spent casing in there, I had to mortar the rifle to get it out, just like I have to mortar my ar15 at the range when I get an FTE with steel cased ammo.

    But I don't want to talk about my rifle and problems with steel case ammo. I would like to hear about other ar15 rifle owners and there findings after doing this so called "test" with ammo at home.

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    If you are in doubt, just have someone ream the chamber for you. That would be the best way to insure it's the proper spec and not guess doing what you plan to do. You can't duplicate the forces applied to the cartridge in a safe manner. Nobody would want you injured trying to "push" the cartridge in.

    Be safe

    Mark
    GET IN YOUR BUBBLE!

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    The chamber spec may be to the nearest thousandth, but the reamers and gauges used to cut and inspect the chamber are precision ground to 0.00001 or better. With these tolerances, one has to consider even small temperature changes and inspection gauges and gauge blocks are never supposed to held by someone not wearing gloves. My guess is that ammo is made to a larger tolerance than the chamber. What I was taught as far metrology is that the instrument used for inspection must have a discrimination less than or equal to 1/10 of the total tolerance of the piece to be measured.
    For example if the part I'm measuring has a tolerance of +/- 0.005, the total tolerance is 0.010. Therefore i need an instrument that measures at least 0.001 for my inspection to be valid.

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    Quote Originally Posted by Eric D. View Post
    What I was taught as far metrology is that the instrument used for inspection must have a discrimination less than or equal to 1/10 of the total tolerance of the piece to be measured.
    For example if the part I'm measuring has a tolerance of +/- 0.005, the total tolerance is 0.010. Therefore i need an instrument that measures at least 0.001 for my inspection to be valid.
    You are correct sir!

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    Quote Originally Posted by Crow Hunter View Post
    You are correct sir!
    Absolutely correct. 10% rule of discrimination is the standard.

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    Quote Originally Posted by Eric D. View Post
    The chamber spec may be to the nearest thousandth, but the reamers and gauges used to cut and inspect the chamber are precision ground to 0.00001 or better. With these tolerances, one has to consider even small temperature changes and inspection gauges and gauge blocks are never supposed to held by someone not wearing gloves. My guess is that ammo is made to a larger tolerance than the chamber. What I was taught as far metrology is that the instrument used for inspection must have a discrimination less than or equal to 1/10 of the total tolerance of the piece to be measured.
    For example if the part I'm measuring has a tolerance of +/- 0.005, the total tolerance is 0.010. Therefore i need an instrument that measures at least 0.001 for my inspection to be valid.
    Meaning to us lay people that sticking a round in the chamber and trying to shake it loose is in no way an accurate gauge of one's chamber?
    Mobocracy is alive and well in America.*
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    Correct.

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    Meaning to us lay people that sticking a round in the chamber and trying to shake it loose is in no way an accurate gauge of one's chamber?
    Correct.
    OK but why would a chamber difference of a couple thousandths of an inch dictate extraction reliablity so long as the chamber dimensions are within tolerances?

    If a steel cased cartridge doesn't "spring back" the way brass does, then wouldn't there be no difference between a "tight" chamber and a "correct" chamber in terms of extraction? Consider in both chambers, that the casing would be formed into the shape of the chamber and not able toretract like brass, therefore having no difference in extraction because the surface tension of the spent steel casing against the chamber walls would theoretically be the same.

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