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Thread: Facing an upper receiver ?

  1. #21
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    Quote Originally Posted by Rascally View Post
    The collection of "random parts taken from a bin" seldom leads to really accurate results, however. Isn't that why a really good 1911 will be full of hand-fitted parts? Sometimes costing as much as or more than the original gun? "Acceptable accuracy and function" mean different things to different people.

    And while if may be true that "big gains in accuracy don't often come from one simple operation", those big gains can come from a series of small operations, all working to the same end. Any hand loader can tell you how large a difference can be had from a small
    .2 grain change in loading, or a small change in bullet depth, or changing primers or brass. It can and does make the difference between .5 MOA and 1.5 MOA.

    In light of these things, why would you not do something so easy and simple that can nudge you toward your goal?

    I recently completed an upper built with a BCM receiver. They certainly nailed the tighter fit for the barrel extension. But the front of the receiver was not perpendicular to the bore. It is now...
    I don't want you to think I was saying don't do it, I was merely pointing out that it may not do wonders, at no point did my post say, as others did, hey you are wasting your time. I was writing that as a guy who has spent hours rubbing clutch pressure plates on my surface plate to get a smoother engagement on our racing kart clutches - it didn't make us winners, but every bit helps, I don't think I wasted my time on that.

  2. #22
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    FWIW, I don't lap any receivers as I don't trust the tool or the method. It would be better served setup properly in a lathe and I've had a couple done by smiths who were familiar with the setup. That's sort of a PITA, of course. What I do now is pick a known, quality upper, install the barrel and barrel nut torqued to 40 lb ft and take it to the range. If it's not grouping properly I'll increase the torque 10 ft lbs and shoot again until I've hit an upper limit of 70 lb ft (sometimes 80 if trending in the right direction). If it's still not grouping properly, I'll try a different upper and repeat the process. I use two handguards with barrel nuts that do not require indexing: a 13" Geissele MK2 or a 12" DD Mother-Effer (MFR). These have pretty generous internal dimensions for most gas block and barrel setups and in the case of the Daniel Defense, it's short enough that a rifle-length gas block will extend beyond the rail.

    Do not forget to factor the length of the barrel nut tool into the torque equation.
    .
    Last edited by Warg; 07-16-15 at 16:05.

  3. #23
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    The problem I see with lapping the upper barrel face is if you cut through the anodizing you now have bare aluminum in contact with steel, and the potential for corrosion to set in.

    For match guns with someone who can hold the X ring at 600 yards, yeah, it is probably worth it. For the average duty weapon, little point.

  4. #24
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    Quote Originally Posted by Warg View Post
    FWIW, I don't lap any receivers as I don't trust the tool or the method. It would be better served setup properly in a lathe and I've had a couple done by smiths who were familiar with the setup. That's sort of a PITA, of course. What I do now is pick a known, quality upper, install the barrel and barrel nut torqued to 40 lb ft and take it to the range. If it's not grouping properly I'll increase the torque 10 ft lbs and shoot again until I've hit an upper limit of 70 lb ft (sometimes 80 if trending in the right direction). If it's still not grouping properly, I'll try a different upper and repeat the process. I use two handguards with barrel nuts that do not require indexing: a 13" Geissele MK2 or a 12" DD Mother-Effer (MFR). These have pretty generous internal dimensions for most gas block and barrel setups and in the case of the Daniel Defense, it's short enough that a rifle-length gas block will extend beyond the rail.

    Do not forget to factor the length of the barrel nut tool into the torque equation.
    .
    different strokes for different folks

    it works for me but I can understand your theoretical arguments

  5. #25
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    Quote Originally Posted by Warg View Post
    FWIW, I don't lap any receivers as I don't trust the tool or the method. It would be better served setup properly in a lathe and I've had a couple done by smiths who were familiar with the setup. That's sort of a PITA, of course. What I do now is pick a known, quality upper, install the barrel and barrel nut torqued to 40 lb ft and take it to the range. If it's not grouping properly I'll increase the torque 10 ft lbs and shoot again until I've hit an upper limit of 70 lb ft (sometimes 80 if trending in the right direction). If it's still not grouping properly, I'll try a different upper and repeat the process. I use two handguards with barrel nuts that do not require indexing: a 13" Geissele MK2 or a 12" DD Mother-Effer (MFR). These have pretty generous internal dimensions for most gas block and barrel setups and in the case of the Daniel Defense, it's short enough that a rifle-length gas block will extend beyond the rail.

    Do not forget to factor the length of the barrel nut tool into the torque equation.
    .
    The point was recently made in another thread that you are supposed to have the barrel nut tool in line, and that's taken into account with the torque values given.

  6. #26
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    Great discussion so far.
    Well, I have obtained the low cost components of the upper so far.
    BCM4 upper, BCM bcg and mod4 ch.

    I am going to face the receiver with the Brownells tool and take pic's .

    In theory, the tighter barrel extension and squaring the receiver will take care of the barrel installation.

    No timing of the barrel nut involved cause it will be free floated.

    Not worried about the barrel being set back to cause feed ramp issues.
    Upper will be single loaded only when complete.
    (please do not bring up slam fires...)

    Next is barrel, gas tube and gas block and then free float tube.

    Clarence

  7. #27
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    Quote Originally Posted by AM-15 View Post
    Great discussion so far.
    Well, I have obtained the low cost components of the upper so far.
    BCM4 upper, BCM bcg and mod4 ch.

    I am going to face the receiver with the Brownells tool and take pic's .

    In theory, the tighter barrel extension and squaring the receiver will take care of the barrel installation.
    Put the barrel in the upper and slide it all the way in firmly. First observe, then measure the gap on all sides at the flange.

    If it's so small you cannot measure the difference with a feeler gauge, then I would not face it.

    If the difference is noticeable, the upper is out of spec and I'd exchange it.

    Personally, I find the facing argument unicorn tears from smiths. Seen too many rifles shoot well without it and one mfg/designer I trust has explained to my satisfaction how the design allows for slight deformation of the AL face under the barrel nut torque. IE: unequal bolt thrust is a myth unless the upper is significantly out of spec. Especially true with tight extension to upper fit, the extension cannot cant!

    With in spec parts, this is wasted effort on carbines. $600 bull barrel with $1k glass, shooting match ammo, I might would consider it.

  8. #28
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    Quote Originally Posted by BufordTJustice View Post
    However, can ensuring that the lugs of the bolt bear equally on the barrel extension equal greater reliability?
    Lapping the extension on the upper receiver ensures no such thing. You'd have to assume that the bolt and barrel extension are perfect. That lapping tool is for shade tree gunsmiths. The process is appealing to a certain crowd because there's nothing else that can be smith'd in the shade of said tree to really improve accuracy.

  9. #29
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    Quote Originally Posted by H Wyman View Post
    Lapping the extension on the upper receiver ensures no such thing. You'd have to assume that the bolt and barrel extension are perfect. That lapping tool is for shade tree gunsmiths. The process is appealing to a certain crowd because there's nothing else that can be smith'd in the shade of said tree to really improve accuracy.
    Finally someone with common sense... I love the "shade tree" reference. I'll bet 99.9% of those who buy the lapping tool have NO way to determine if the receiver face was square before lapping or after. Shade tree gunsmiths..... I love it!

  10. #30
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    Quote Originally Posted by GH41 View Post
    Finally someone with common sense... I love the "shade tree" reference. I'll bet 99.9% of those who buy the lapping tool have NO way to determine if the receiver face was square before lapping or after. Shade tree gunsmiths..... I love it!
    Agreed. Additionally, one has to guarantee the barrel nut is square and that internal dimensions of the receiver are sufficiently tight & square to ensure the lapping face of the tool of the tool is correctly setup.

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