How many barrel shims are too many on AR Barrel Nut

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  • whbonney26

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    I am building an AR and have built over 30 and this is the first time that I have ever not been able to get the barrel nut/gas tube to line up.

    I am using Aero Precision's BAR barrel nut with their upper and their handguard. It came with like 5 shims and none of them get the barrel nut close enough to line up. It always falls either too far from the gastube hole or too close so when its torqued it passes it up.

    I am stumped as to what to do. It looks like it needs more barrel shims.
     

    thperez1972

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    The one time I used their BAR barrel nut I ran into this issue. I think my solution was to stop right below the minimum of the torque range. I couldn't seem to find the right combination of barrel shims either. I've used their Enhanced upper on a couple of builds and would gladly pay the extra money for the built in BAR handguard attachment points.
     

    whbonney26

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    The one time I used their BAR barrel nut I ran into this issue. I think my solution was to stop right below the minimum of the torque range. I couldn't seem to find the right combination of barrel shims either. I've used their Enhanced upper on a couple of builds and would gladly pay the extra money for the built in BAR handguard attachment points.


    Yeah, I wish I would have just got that upper to begin with. One shim not enough, two or more shims and it just messes up the alignment even further.

    I cant even seem to get close enough for a min torque. Anything more than hand tight and it over turns.
     

    thperez1972

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    I want to say it took me 20-30 of messing with it before I got to a place I was confortable.
     

    ozarkpugs

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    Have you lapped the upper ? If not you may need to take a couple of thousandths off to get it tried up and that could make a lot of difference .

    Sent from my Moto E (4) using Tapatalk
     

    rcm192

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    Have you lapped the upper ? If not you may need to take a couple of thousandths off to get it tried up and that could make a lot of difference .

    Sent from my Moto E (4) using Tapatalk

    Lapping is easy and you can get it just right. It's the method I use.

    https://www.brownells.com/gunsmith-...16-upper-receiver-lapping-tool-prod20220.aspx

    p_080000182_1.jpg
     

    whbonney26

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    Thanks. I didn't lap it this time around. I never really thought about doing that for an AR build. This is the first time I have ever had a problem with a barrel nut not lining up fairly easy. I have use one shim or so a couple times but usually got it lined up easily.

    I messed with that BAR nut so much yesterday till I said screw it and ordered an enhanced upper. I will use that other upper on the next build I guess.

    Lapping didn't even cross my mind and I have the tools to do it.

    Yesterday just wasn't my day and this project owned me.

    :owned:
     

    chrisdcd

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    I use Aero for most builds. Their chassis anyway. I really haven't run into it personally, but I would say use as many as it takes. If you go with the enhanced or the Atlas line from Aero you don't have to worry about it. They are a little more pricey, but much easier to deal with. Torque spec is 30-80 ft/lbs, which is a huge variance, but there is a reason why, and it's because of the exact issue you are having. I think lapping is a good idea. I don't know how much you really take off of the receiver doing that, never measure it, but it's always good to true it up. As many as it takes. I had a guy that bought an Aero kit and he ran into that issue. I wouldn't buy the kits, especially if they come from Delta Team Tactical. I'm not even sure why Aero allows Delta to market their stuff with their name on it. It degrades the product as far as I'm concerned. That's another topic though.
     

    jkingrph

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    I never had the problem of aligning the nut to gas tube. I did use the Brownells lapping tool on a couple of builds and was surprised that the face of the upper receiver where the barrel seats is not very flat. You basically apply a little valve grinding compound to the receiver face and then spin the lapping tool and check. Grind until you get a uniform silver color and you are done.
     

    redbaron8

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    Hi all. Not bragging here but I've spent the last five years building AR15s, using every single brand of handguard on the market. From Cheap to Ultimate AR high dollar stuff. Shims were rarely needed, but when they were usually 4-5 max did the job. I agree that lapping is a good idea, but it was rarely done/needed in a production environment. And here is some food for thought.....if you can get at least a good 35-40 ft.lbs on the nut, with the gas tube going through the barrel nut, you're good to go. Here's why. The gas tube essentially acts as a locking key for the nut. It won't allow the barrel nut to unscrew and loosen up. Have done tons of uppers that fell into this circumstance, and to my knowledge, all of them are still out there slinging lead with aplomb.
     

    thperez1972

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    Hi all. Not bragging here but I've spent the last five years building AR15s, using every single brand of handguard on the market. From Cheap to Ultimate AR high dollar stuff. Shims were rarely needed, but when they were usually 4-5 max did the job. I agree that lapping is a good idea, but it was rarely done/needed in a production environment. And here is some food for thought.....if you can get at least a good 35-40 ft.lbs on the nut, with the gas tube going through the barrel nut, you're good to go. Here's why. The gas tube essentially acts as a locking key for the nut. It won't allow the barrel nut to unscrew and loosen up. Have done tons of uppers that fell into this circumstance, and to my knowledge, all of them are still out there slinging lead with aplomb.

    With the barrel nut the OP is referring to, that is the challenge. A lot of barrel nuts have 20 or so places for the gas tube to fit. That means the most you should have to tighten it once you hit the minimum 30 ft-lbs of torque is 18 degrees. If you start lining it up at 30 ft-lbs, you're almost assured to have it indexed before you hit the 80 ft-lb upper torque limit. (I realize these values are not agreed upon by everyone but they are a widely accepted guideline.)

    The Aero Precision BAR barrel nut, on the other hand, has 4 indexing points. More torque won't get you from right past one to the next one. Shims or lapping will almost always be necessary. The instructions even have a math test to help you figure out what shims may work.

    aprh100268-ar15-bar-barrel-nut.jpg


    bar-barrel-nut-instructions_Page_1.jpgbar-barrel-nut-instructions_Page_2.jpgbar-barrel-nut-instructions_Page_3.pngbar-barrel-nut-instructions_Page_4.jpg
     
    Last edited:

    asianpersuasion

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    I had a stretch 16" barrel that shot like ****. Changed mounts for scope ect. Ended up calling Stretch and they said lap upper. Fixed all my issues. So now I lap everything to be safe

    Sent from my SM-G965U using Tapatalk
     

    A5BLASTER

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    I lapp every reciver I use. No matter how much they cost. Not only does it help with getting things torqued. But it makes everything nice and square when the bolt is locking and unlocking.

    I only run grendel rifles and doing this above I have never broke a bolt or extractor.

    A simple trick to trimming a barrel nut. Don't use a barrel nut that the gas tube has too go through. Much more simpler and no chance the tube will touch the barrel nut and cause binding issues with the bcg and wreck your accuracy.

    I also follow the balanced torque theory. You can Google that and read up on it. I have seen a real improvement in my consistent group tightness since useing this practice.
     

    Magdump

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    I’ve had to drill alternate gas tube pathways thru barrel nuts at times. Mostly on the off brand or chinese rail kits. Even had to enlarge a few holes on some of the aluminum multi hole nuts because the gas tube wouldn’t pass thru. Without the press and vise I have I prolly wouldn’t attempt it tho. I have used shims but I’d rather drill where it will work.
    I’m the guy people bring their screw ups to apparently. I’ve not once let someone walk away without the fix, but it’s a chore sometimes. I beg people to do some research and look for rails that use hardware that works, like steel low profile barrel nuts that the gas tube doesn’t pass thru or that use a mil spec nut. Hopefully the demand will create a standard! Stranger things have happened.
    So, research and spend wisely. It may save you a lot of time and dollars down the road. Personally I’d rather spend the extra time and money on **** that works than buying twice or spending a day trying to make **** work.
     

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