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Thread: Lower flex when torquing buffer tube

  1. #1
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    Lower flex when torquing buffer tube

    Hi all, I just finished up my SHTF SBR and I had a couple of questions. I used a bev block in the magwell and the lower receiver (Aero M4E1 Liberty) flexed A LOT when torquing the castle nut to 40#. I stopped cranking when I noticed and used my leg against the buffer tube to provide more support and then torqued it to 40# without any obvious issue. The buffer tube is straight, the lower looks straight and I can't visually detect any cracks or anything...

    I know Colt has some proprietary alignment jig they use, but am wondering if that kind of flex is ok. I'm guessing not.

    My two questions are:

    1. Do I need to be concerned with any damage or weakening of my lower receiver from the flex? I had already installed the trigger etc. as well, could there be issues with the parts or the pin holes in the lower?

    2. Is there a better way to do this?

    Not only does this lower have my SBR stamp but it's also a limited run from last July 4th with a really pretty "Liberty" shield rather than the usual Aero logo, so I'm very concerned about having damaged or weakened it in a way I lack the expertise to notice.

    Thank you!

    And yes I searched.
    Last edited by Superhero; 09-01-21 at 10:13.

  2. #2
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    Yeah I wouldn’t twist a receiver like that.

    I hold the tube by the rail in a vice, and hold the receiver from spinning by holding it a big adjustable wrench on the flat that goes into the grip.

    I torque to about 30#, lubed with oil, stake in two slots.

    It’s not to spec, but I’ve never had one come loose in years of building some high round count lowers.

  3. #3
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    Yeah I wouldnít twist a receiver like that.

    I hold the tube by the rail in a vice, and hold the receiver from spinning by holding it a big adjustable wrench on the flat that goes into the grip.

    I torque to about 30#, lubed with oil, stake in two slots.

    Itís not to spec, but Iíve never had one come loose in years of building some high round count lowers.

  4. #4
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    Thank you for the response!

    That sounds like a great way to install it. I'd rather damage a buffer tube than my lower receiver.

    I didn't lube the threads, though it likely had some CLP on it.

    I plan on staking it after i do a function test. Do you think it would be advisable to reinstall the buffer tube?

    Is there any kind of metal fatigue or anything I should be concerned with?





    Quote Originally Posted by 17K View Post
    Yeah I wouldn’t twist a receiver like that.

    I hold the tube by the rail in a vice, and hold the receiver from spinning by holding it a big adjustable wrench on the flat that goes into the grip.

    I torque to about 30#, lubed with oil, stake in two slots.

    It’s not to spec, but I’ve never had one come loose in years of building some high round count lowers.

  5. #5
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    Ive installed thousands of buffer tubes using a receiver block and then a reaction block. Some twist can occur but its never been an issue. I also lube the threads with anti-seize
    "your AR is shit, change my mind" - Will Larson

    I make work horses, not show ponies.

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    Quote Originally Posted by Steve-0- View Post
    Ive installed thousands of buffer tubes using a receiver block and then a reaction block. Some twist can occur but its never been an issue. I also lube the threads with anti-seize
    Did the receiver block utilize the magwell?

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    Quote Originally Posted by Superhero View Post
    Thank you for the response!

    That sounds like a great way to install it. I'd rather damage a buffer tube than my lower receiver.

    I didn't lube the threads, though it likely had some CLP on it.

    I plan on staking it after i do a function test. Do you think it would be advisable to reinstall the buffer tube?

    Is there any kind of metal fatigue or anything I should be concerned with?
    I think it’s ok. The castle nut is just a jam nut to keep the tube from being loose. It doesn’t do a whole lot. 40 ft/lbs is way overkill IMO.

    7075 is tough, I highly doubt you hurt anything.

  8. #8
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    Quote Originally Posted by opngrnd View Post
    Did the receiver block utilize the magwell?
    Yes, its an old brownells one. The reaction block is pretty kickass but having to slide the wrench on prior to insertion then use the grip instead of a stock to apply back pressure is a pain in the ass.
    "your AR is shit, change my mind" - Will Larson

    I make work horses, not show ponies.

  9. #9
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    Thanks for the input. I'm definitely a perfectionist so the knowledge is appreciated!

    fwiw I spoke with geissele and they stated they torque to 40#, as does Daniel Defense.

  10. #10
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    Quote Originally Posted by 17K View Post
    40 ft/lbs is way overkill IMO.
    That torque is what keeps reasonable knocks on the stock from twisting the receiver extension. Staking and bump on the end plate are not strong enough by themselves.

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