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Thread: one-piece gas rings and M4A1

  1. #31
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    Alright folks,

    Measured eight different bolt carriers out of Colt M4A1's today. Four of the eight I.D.s measured .5275". The rest varied from .5249 through .5280. Regardless, it looks like a difference of slightly over 20 thousandths compared to the .503" of the McFarland rings. That would explain the looseness.

    Well, unfortunately, it looks like a no-go on the McFarlands and these M4A1 carriers unless I'm missing something.

    Again, thanks for the info and advice, folks.
    Last edited by patrolman; 03-01-10 at 18:25.

  2. #32
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    That is true. The other method is one that Colt or Ken Elmore came up with and works equally as well. I think it is actually a better method myself. YMMV

    Quote Originally Posted by 5pins View Post
    The proper way to test the gas rings is to remove the firing pin and cam pin then hold the carrier with the bolt pointed to the ground. If the bolt fall out then the gas rings need to be replaced.

    Chapter 3 page 0011-6 of the TM 9-1005-319-23&P



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  3. #33
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    Quote Originally Posted by patrolman View Post
    Alright folks,

    Measured eight different bolt carriers out of Colt M4A1's today. Four of the eight I.D.s measured .5275". The rest varied from .5249 through .5280. Regardless, it looks like a difference of slightly over 20 thousandths compared to the .503" of the McFarland rings. That would explain the looseness.

    Well, unfortunately, it looks like a no-go on the McFarlands and these M4A1 carriers unless I'm missing something.

    Again, thanks for the info and advice, folks.
    ?????
    Remember that the carrier bore has two chambers,and a port at the very back for the bolt tail which works as a mechanical seal basically.
    The first and larger chamber at the front of the carrier bore is where the bolt bearing band resides.Then you have a step transition into the smaller rear chamber in which the gas rings reside.
    I checked some carriers at the front chamber and all are around .5280"-.5300"+/- throughout a mixed bunch from LMT,Armalite,DD,BCM and Spikes..Unfortunately I do not have a bore gauge small enough to fit the carrier bores at the moment,and a caliper aint gona reach..
    I cant find any internal dimension of the carriers online,but if I were to take a shot in the dark I'd say the gas ring or second chamber of the carrier bore will be close to my used McFarland rings which have a "fit like a glove" feel...and that being roughly or slightly smaller I.D than the .4970"-.4985" my rings measure.
    So if your measuring the front chamber to gauge gas ring fit,it has nothing to do with what the gas rings will do.If your carriers have a single size chamber all the way in,then you have a major malfunction.
    Last edited by Blankwaffe; 03-02-10 at 07:07. Reason: ETA
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  4. #34
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    Quote Originally Posted by Iraqgunz View Post
    That is true. The other method is one that Colt or Ken Elmore came up with and works equally as well. I think it is actually a better method myself. YMMV
    Hey IG.

    So the "stand the BCG bolt face down on a table" gas ring test came from Colt or Ken Elmore?
    I was wondering where I read that technique sometime back.
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  5. #35
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    As far as I know. I learned that method the first time I took his course about 5 years or so ago.

    Quote Originally Posted by Blankwaffe View Post
    Hey IG.

    So the "stand the BCG bolt face down on a table" gas ring test came from Colt or Ken Elmore?
    I was wondering where I read that technique sometime back.



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  6. #36
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    The first and larger chamber at the front of the carrier bore is where the bolt bearing band resides.Then you have a step transition into the smaller rear chamber in which the gas rings reside.
    Indeed. Thanks for setting me straight on that.

    Next wild speculation: I figure that the slight variance at the front of the carrier bore will translate to a slight variance in the chamber where the rings reside, hence the looseness of the one-piece rings in the M4A1 carriers in question.

    I should have the rings from G&R by the end of this week and I'll try those before giving up. I'll let y'all know how it goes.

    Again, thank you all for the info and advice.

  7. #37
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    Yeap,all the carriers seem to vary slightly in I.D between each other and in how perfectly round the bore is,which is probably related to the chrome as mentioned before.
    The front chamber being somewhat large only seems to cause the bolt to have some end play,particularly when fully extented in out of battery position.Which I kinda prefer,as I have a couple carriers that are very tight fit in the front chamber with the bolts bearing band and I suspect would develop resistance when fouled heavily.
    Otherwise no issues Ive seen.
    The gas rings fit so in the ring groove of the bolt that they have some float similar to what is seen in an engines piston and rings.So I dont see that as having any issue on performance.
    Hopefully the rings from Grant will get you up and running.
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  8. #38
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    Quote Originally Posted by Iraqgunz View Post
    As far as I know. I learned that method the first time I took his course about 5 years or so ago.
    Quib asked me sometime back where I had picked up that gas ring technique and for the life of me I could not remember the exact source.I do remember that the department armorer used that technique and is probably where I picked it up.I had no idea that Ken Elmore taught the technique...puts even more value on it.
    I agree with it being a better technique...
    Thanks for the info bro,and be safe over there.
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  9. #39
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    The front chamber being somewhat large only seems to cause the bolt to have some end play,particularly when fully extented in out of battery position.Which I kinda prefer,as I have a couple carriers that are very tight fit in the front chamber with the bolts bearing band and I suspect would develop resistance when fouled heavily.
    Makes sense. I figured the end play also allowed the bolt lugs to "wear in" to the barrel extension over time. I noticed on the carbines with a healthy number of rounds downrange that the wear on the bolt lugs is similar, but unique.

    Much appreciate the info, Blankwaffe.

    By the way, have any of y'all successfully run the one-piece rings on an M4A1?

  10. #40
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    Quote Originally Posted by Iraqgunz View Post
    That is true. The other method is one that Colt or Ken Elmore came up with and works equally as well. I think it is actually a better method myself. YMMV
    We used that method when I was in the Army. We knew it was incorrect, as far as the TM was concerned, but it was easier and quicker.

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