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  1. #1
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    AR-15 Barrel Swap

    I picked up a Rosco 10.5" barrel pre-pandemic and decided to swap out the 10.3" BA Hanson barrel that was previously installed. There is nothing wrong with the BA barrel, but I've been wanting to test this Rosco barrel out and didn't want to bother sourcing parts right now. I'm not an expert and don't claim to be one. I learn from my mistakes and don't mind passing along info if can prevent anyone else from making the same mistakes I did. For the sake of documentation and discussion, what is shown is a way and not the way. To accomplish this fairly simple task, I used a myriad of tools, such as:

    Bench Vise
    Torque Wrench (ft/lbs)
    Torque Wrench (in/lbs)
    Midwest Industries URR
    Wheeler Clamshell Upper Vise Block
    BCM KMR Barrel Nut Wrench
    FCD JMW (Joint Muzzle device Wrench)
    T-Handle Bit Driver
    Various Bits (Torx and Hex)
    Wood Burner with Pointed Tip
    Roll Pin Holder Punch
    Assorted Pin Punches
    Polymer Grooved Vise Jaws
    Double Sided Mallet
    Loctite 271
    Loctite 243
    Aeroshell 64
    Cleaner/Degreaser
    Otis Cleaning Brushes

    Prior to disassembling the upper receiver, when the barrel had originally arrived, I checked headspace with a good bolt. Using a bolt vise and punch makes disassembling and assembling the ejector very easy. With the ejector and extractor removed, I can then check the barrel with a .223 GO, 5.56 GO, .223 NO GO, and FIELD (Maximum) gauge.





    To begin the disassembly, I placed the upper receiver on the Midwest Industries URR, which slide into the receiver like a bolt carrier and has a square end to clamp in the vise. The major difference between the MI URR and the Geissele Reaction Rod is that it has a "sail" on top that locks into the charging handle channel as well as the lugs that lock into the barrel extension. This ensures the upper receiver and the barrel extension are held securely while the barrel nut is tightened and loosened. The other advantage of the MI URR is that it gives you an excellent stand to hold the upper receiver while you work on it. First step was to remove the BCM MCMR Handguard by removing the two crossbolts. The handguard is a fairly tight fit, so I had to tap the handguard off with a soft mallet.



    Here you can see the lugs cut into the MI URR that interface with the barrel extension. Since the gas block and tube are still installed, flipped the upper upside down makes accessing the barrel nut much easier.



    Another advantage of the MI URR is the ability to hold the barrel in place while you can tap the upper receiver off. The sail on the top of the MI URR is slightly shorter than the full length of the charging handle channel so it does not interfere with the gas tube on a complete upper receiver. This added space allows the receiver to slide rearward on the URR when removing tightly fit barrels. A few light taps is all it takes.



    Now to the gas block, which on this particular example has two set screws as well as a coiled spring pin used as a cross pin. Since the set screws were installed with Red Loctite, they must be heated to be removed. This is easily accomplished with a wood burner and pointed tip. Heat the screws directly for 30 seconds and they will break free. After removing both set screws, I place the barrel and gas block on my grooved vise jaws to hold the gas block while I tap out the cross pin with a flat faced pin punch. You don't want to use a roll pin punch with a nub on the end when using coiled spring pins as they will expand and split.





    With the gas block set screws and pins removed, the next step is to remove the muzzle device. I am not a fan of using clamshell blocks or other upper receiver devices to remove muzzle devices, because the barrel is threaded into the barrel extension and I have no reason to apply torque in a manner that can potentially loosen the barrel from the extension, shear the index pin, or damage the upper receiver. Clamping the barrel itself ensures no stress is seen on the upper receiver, index pin, or barrel extension.



    Now that the original barrel has been disassembled, the upper receiver now has to be cleaned and degreased of any carbon and Aeroshell remnants.



    These are the new parts being used along with the original upper receiver and barrel nut:
    Rosco Mfg. Bloodline 10.5" 5.56 Barrel
    Forward Controls Design GBF (Low Profile Gas Block)
    Sionics Melonite Gas Tube



    When I'm installing a barrel that already has a tight fit, I prefer to apply a small amount of Aeroshell 64 to the barrel extension itself prior to inserting it into the upper receiver. After installing the barrel, the upper receiver threads must be coated with Aeroshell 64. There are other greases that can be used here, but you want to avoid anything with graphite mixed in. For the price of most greases, I just stick with the TDP spec Aeroshell 64 (formerly 33MS).




    This is where you follow the manufacturer's installation instructions for your chosen handguard. BCM specifies 40-50 ft/lbs for their KMR barrel nuts. This is where most people get confused, because the torque value in the TM specifies 30-80 ft/lbs. People need to understand that 30-80 ft/lbs is the torque spec used to achieve proper alignment of a USGI steel barrel nut without the use of shims. There is no reason to torque an aftermarket free float barrel nut beyond what the manufacturer specifies in their installation instructions.

    The next step is to install the gas tube into the gas block. I prefer to do this by placing my gas block in the grooved vise jaws to keep it steady. There are gas block jigs and blocks available to do this, but I already own the vise and vise blocks, so I make it work. I'm using coiled spring pins rather than slotted spring pins, so making use of a roll pin holder punch is very useful. Once the pin is started, I use a larger diameter flat faced pin punch to drive the coiled spring pin into place. If I am using slotted spring pins, I can use the nubbed roll pin punches, which do well seating slotted pins.



    After installing the gas tube, it's now time to install the gas block on the barrel. Rosco is one of the few cheaper priced companies that dimples their barrels in house, so there is no need for a dimpling jig. The gas block I'm using includes a set of knurled cup point set screws of the appropriate length, so I degrease them and apply a very small amount of Loctite 271. You can also use Rocksett and Vibratite Hot-Lock. Both are good up to 2000 degrees Fahrenheit.

    Note: Knurled Cup Point Set Screws are single use screws and should be discarded when removed. It's also not worth the effort to remove any previous threadlocker from such an inexpensive item.

    Both screws are torqued to 25 in/lbs.





    Once the gas block is assembled, you can then follow the manufacturer's installation instructions for your muzzle device. I am using a Dead Air Flash Hider with Surefire shims, so I placed my barrel in the vise jaws, selected the proper shims to time the flash hider, and torqued to 25 ft/lbs. If using an A2 flash hider, you can use a crush washer and tighten until the flash hider is timed and the crush washer has begun to compress.

    The final step is to reinstall the handguard, clean and degrease the hardware, and apply Loctite 243 or Vibratite VC-3. I'm currently out of Vibratite VC-3, so I used Loctite 243.



    Here is the finished product.


  2. #2
    Moving forward

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    Good write up and pics. What was the total time for the project?

  3. #3
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    Quote Originally Posted by Tboy View Post
    Good write up and pics. What was the total time for the project?
    I worked on it in sections over two days before and after the hurricane passed. I would say total time was maybe 3 hours, but that's because I am overly obsessive about keeping my workspace clean and ensuring I have everything cleaned, degreased, and dry prior to installing anything. If it were not for the disassembly, I could likely build the upper in under an hour. There are no rewards for going fast when you're not being paid to do it.

  4. #4
    On Target

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    when people tell me they use thread lock.I wont buy it.And when I do
    see it,,I never put it back on.Been shooting ar-15s 30 years,never an issue..
    Line it up right,Make it tight,ita b aight!!!
    Last edited by TrapperT; October 30th, 2020 at 09:17 AM.

  5. #5
    Marksman

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    nice post! glad you put all the numbers in there. I'll have to probably put together my next upper in a similar manner (instead of good'n'tight for torque specs). Let me know how you like the Rosco barrel. I have a Rosco in 14.6", but it's a midlength gas system and their current 14.6" are carbine length. I'm debating swapping because my current set up is picky about ammo and reliable cycling.
    Really?

  6. #6
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    Quote Originally Posted by bush_hog View Post
    nice post! glad you put all the numbers in there. I'll have to probably put together my next upper in a similar manner (instead of good'n'tight for torque specs). Let me know how you like the Rosco barrel. I have a Rosco in 14.6", but it's a midlength gas system and their current 14.6" are carbine length. I'm debating swapping because my current set up is picky about ammo and reliable cycling.
    The carbine length setup is going to have longer dwell time and should run more efficiently with a smaller port. I know they have been reducing port sizes to run better suppressed and get out of that one size fits all category. The port on my 10.5 is much smaller than the 10.3 Hanson, but sadly I don’t have the pin gauges to check it.

    Even the Harbor Freight torque wrenches with +/- 5% accuracy are better than the Gootentite method. It’s also added peace of mind knowing it was installed more accurately.

  7. #7
    Marksman

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    Quote Originally Posted by bush_hog View Post
    nice post! glad you put all the numbers in there. I'll have to probably put together my next upper in a similar manner (instead of good'n'tight for torque specs). Let me know how you like the Rosco barrel. I have a Rosco in 14.6", but it's a midlength gas system and their current 14.6" are carbine length. I'm debating swapping because my current set up is picky about ammo and reliable cycling.
    I love my mid-length gas 5.56 upper it shoots nice and smooth with no issues.

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