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Thread: AR Assembly QC Advice

  1. #11
    Quote Originally Posted by MistWolf View Post
    I'm not certain about the torque spec. I tighten the set screws by feel, but I've been an aviation technician for more years than I care to admit and have experience. Dimple the barrel for the set screws. Use the toothed set screws sold by Forward Control Designs and stake the set screws in place. Don't use red Locktite unless you want to have to drill out the set screws to remove them. The receptacles of head head screws are very easy to strip out.
    I don't recall if you have your parts yet.

    On the gas blocks I use the Geissele Carbon Steel Gas Block sold by ALGDefense (his wife's company): https://algdefense.com/carbon-steel-gas-block.html

    The reason I like this particular block is because of the straight forward installation and the fact that it is super easy to pin the gas block so it absolutely will not move. I would recommend this if you have a drill press or know someone who does. Here are the instructions so you can see:

    Go to Super Gas Block Instructions and download the PDF, extremely detailed, down to McMaster-Carr part number for the drill bits needed. Good stuff.

    There are other gas blocks out there that are already drilled for pinning, but the ALGDefense/Geissele has my vote.

  2. #12
    I highly recommend getting either the Geissele reaction rod or (significantly) cheaper Brownells version if you intend to build an AR or swap a muzzle device. It makes the process of installing barrels and torquing muzzle devices painless.

    Other specialized tools you want to have:
    Castle nut wrench
    Gas tube roll pin installation punch
    Gas tube roll pin removal punch

    Generic helpful/necessary tools:
    Hammer/mallet
    Torch(for removing anything secured with loctite)
    Impact driver with impact rated bits
    Torque wrench and/or driver
    Good 4-6" bench vice


    RE gas blocks: I've always red loctited them on the recommendation of the Sionics armorer I spoke to. Never had a problem with removal. Just hit it with a torch till you see smoke, then use an impact driver with a good bit.

    If I cared about LR precision and my barrel extension had a loose fit to the upper I'd make sure I shimmed or green loctited the barrel in place. Or I'd just hit a quality receiver and barrel and not worry about it.
    Last edited by littlejerry; 09-20-2020 at 11:49 AM.

  3. #13
    Site Supporter OlongJohnson's Avatar
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    Quote Originally Posted by littlejerry View Post
    I highly recommend getting either the Geissele reaction rod or (significantly) cheaper Brownells version if you intend to build an AR or swap a muzzle device. It makes the process of installing barrels and torquing muzzle devices painless.
    I have thought about this. The idea behind the Geissele reaction rod as I understand it is to hold the barrel, so that you counteract the torque applied when tightening the barrel nut and keep the clocking pin from taking all that load in shear. However, the reaction to the torque you're applying is resistance from tightening. It comes from the friction and ramp angle of the threads, as well as from friction around the flat, circular contact of the nut against the forward surface of the barrel extension. If the point is to limit the shear force on the clocking pin and its notch in the upper receiver, you would want to hold on the part that offered the greater reaction torque. It seems likely to me that the friction and ramp angle of the receiver threads will account for a much greater share of the reaction torque than the flat, circular contact of the nut against the forward surface of the barrel extension. So it is logical to me to hold the receiver, not the barrel extension.

    I use one of these:
    https://www.midwayusa.com/product/1007359056?pid=210021

    I have never used the insert, as it's undersized and lame. Instead, I use a chunk of 1-inch diameter drill rod blank (not a drill) -and- (making sure the end is thoroughly deburred) inserted in the UR to prevent it being crushed when clamped in the vise. Also, you'll want to install the forward assist after everything else is done, because the button sticks out just a little farther than the thickness of the block and your vise jaws might want to press against it.

    Quote Originally Posted by littlejerry View Post
    Other specialized tools you want to have:
    Castle nut wrench
    Gas tube roll pin installation punch
    Gas tube roll pin removal punch
    If you happen to be using a BCM free-float handguard, the tool that's included for use with their proprietary barrel nut is actually a castle nut wrench, so you don't need to buy one separately.

    Squirrel Daddy sells roll pin installation punches.

    Home Depot sells ordinary pin punches that are quality and don't include the "gun stuff" tax.

    There's a setup for dealing with the sequence of the front take-down pin and its detent and spring. Worth getting.

    Get a decent-quality torque wrench, not a cheap one. It's a lifetime investment.

    Wear safety glasses. When those little bits go flying, they can end up on the floor behind your work bench, lost in space, or in your eye. In your eye is definitely the worst of the three.

    I take as long as it takes to go over all the plastic bits (grip, buttstock, handguard if not free-float, etc.) and shave off the mold parting lines with razor blade, X-Acto knife, files, sandpaper, etc. It's kinda OCD, but it actually does make a noticeable difference in how things feel when you're handling them, as well as how it looks.
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  4. #14
    Quote Originally Posted by OlongJohnson View Post
    If the point is to limit the shear force on the clocking pin and its notch in the upper receiver, you would want to hold on the part that offered the greater reaction torque. It seems likely to me that the friction and ramp angle of the receiver threads will account for a much greater share of the reaction torque than the flat, circular contact of the nut against the forward surface of the barrel extension. So it is logical to me to hold the receiver, not the barrel extension.
    It's pointless to argue the merit of one over the other because the only way to prevent torque reaction is to hold the receiver and the barrel

    It's kinda OCD, but it actually does make a noticeable difference in how things feel when you're handling them, as well as how it looks.
    Amateurs have OCD. Professionals have CDO. It's like OCD but in the proper alphabetical order. Nonetheless, it's well worth the effort to reshape the grip as needed. The BCM Gunfighter Grip especially so.
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  5. #15
    Site Supporter OlongJohnson's Avatar
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    Quote Originally Posted by MistWolf View Post
    It's pointless to argue the merit of one over the other because the only way to prevent torque reaction is to hold the receiver and the barrel
    Right. Tell us about it if you know of a tool that holds both. I've only seen tools that hold one or the other. It's still possible to pick one that stresses the clocking pin less, rather than more. And save a C-note or a bit more in the process.


    Quote Originally Posted by MistWolf View Post
    Amateurs have OCD. Professionals have CDO. It's like OCD but in the proper alphabetical order.
    I go back and forth on that. I enjoy the joke about CDO, but "compulsive disorder, obsessive" isn't really a thing. "Disorder, obsessive-compulsive" would fit into the backward military formality of putting all the adjectives after the noun, but I've never even heard a soldier or sailor say it that way. Since the accepted phrase is "obsessive-compulsive disorder," it's logical to put the acronym in the corresponding sequence. Otherwise, you're kinda making a hash out of things.

    Maybe the difference is that OCD stops where things are still functional, but CDO abandons functionality for some arbitrarily imposed principle or objective that's unrelated to the original goal.
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  6. #16
    Quote Originally Posted by OlongJohnson View Post
    Right. Tell us about it if you know of a tool that holds both. I've only seen tools that hold one or the other. It's still possible to pick one that stresses the clocking pin less, rather than more. And save a C-note or a bit more in the process.
    I've used both types and I've not found one to be less stressful to the pin than the other.

    It's been awhile since I looked around for an upper tool, but I believe I did find one that held both. I think it was bumping up against $300.

    When working on muzzle devices, I like to use a barrel vise as close to the muzzle as practical.
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  7. #17
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    All I’m going to say here is that I am 100% sure you can shear a barrel extension index pin and unscrew the barrel extension when attempting to remove a muzzle device with a standard reaction rod.

    Geissele makes an advanced reaction rod that also locks in on the ejection port of the upper. This is supposed to relieve the stress on the barrel intel pun.
    Last edited by HCM; 09-20-2020 at 11:05 PM.

  8. #18
    Site Supporter rob_s's Avatar
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    It is much, much harder to source true high quality, or even just in-spec, parts today than even a decade ago. The cash cow that is the AR market has attracted manufacturers turning out garbage for a buck, which in turn has led even some known good manufacturers to get pretty stupid (even just in their marketing). For those of us that have been around awhile it may be “plain t see” that BCM is known good, but to someone asking about assembling their first AR from parts how do you know that BCM is any gooder than Olympic? Particularly when both are using similar marketing speak?

    While there may be more gooderer parts and pieces available, the increase in the number of garbage, suspect, or unicorn jizz parts is even greater still, thus making for a much higher percentage take of garbage than good than in years past.

    Buy all Colt parts, drop in, shoot gun.

    OP I know you said you didn’t want to hear that, but it’s just that easy. Buy good parts, you have no problem. Buy garbage parts and then you get to travel the rabbit hole of buying gas key staking tools, chamber checkers and reamers, pin gauges to verify gas ports... I have all those tools myself but I’ve basically never had to turn a single one loose on a personally owned gun because I bought good guns/parts (read “Colt”) and they just work. I recently deviated and bought a PSA PCC upper and...? Problems.

    Better yet, just buy a known good gun. Buying a known good first gun is a shooters solution. “I’m ‘building’ from parts so that I know the system” is folly. How do you learn the system if you don’t know anything about the system and don’t have a basis for what “right” is? This is route of a tinkerer. “not that there’s anything wrong with that” as Jerry would say, but it’s not a shooter’s solution.
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  9. #19
    Quote Originally Posted by rob_s View Post

    While there may be more gooderer parts and pieces available, the increase in the number of garbage, suspect, or unicorn jizz parts is even greater still, thus making for a much higher percentage take of garbage than good than in years past.

    Buy all Colt parts, drop in, shoot gun.

    OP I know you said you didn’t want to hear that, but it’s just that easy. Buy good parts, you have no problem. Buy garbage parts and then you get to travel the rabbit hole of buying gas key staking tools, chamber checkers and reamers, pin gauges to verify gas ports... I have all those tools myself but I’ve basically never had to turn a single one loose on a personally owned gun because I bought good guns/parts (read “Colt”) and they just work. I recently deviated and bought a PSA PCC upper and...? Problems. .

    I am learning the differences in quality parts vs. crap parts and what makes them different. I understand there are definitive differences.

    So, hypothetical situation:
    Say I have two rifles, one factory and one assembled at home. I then test both with 1000 rounds of various ammunition types with various magazine under various conditions etc. Both have zero malfunctions not related to ammunition or magazines.

    Is there anything specific that would cause the home assembled rifle more likely to have a failure of some component on round 1001 versus the factory gun?

    Non-hypothetically, what part or parts in the above scenario would be most likely to cause a problem? More specifically, excluding quality of parts, what part of the assembly process would be most critical to preventing malfunction? What “QC check” could be done to verify if those critical components were properly interfacing?

  10. #20
    Quote Originally Posted by MistWolf View Post
    It's pointless to argue the merit of one over the other because the only way to prevent torque reaction is to hold the receiver and the barrel
    Quote Originally Posted by OlongJohnson View Post
    Right. Tell us about it if you know of a tool that holds both.
    There was a thread on here a while back that tipped me off to the MI URR:
    https://www.midwestindustriesinc.com...d-p/mi-urr.htm
    It is a buttload of $ for a tool but I tend to look at the cost delta, and the Brownells was $50, so it only cost me an additional $45 to get the ultimate. Plus I intend to be monkeying around with these things till I croak off.

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