MR556 barrel removal
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Thread: MR556 barrel removal

  1. #1
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    Default MR556 barrel removal

    I have been on the fence for a while now on whether or not to get my MR556 barrel turned down. One of my hang-ups was the cost. Just getting a barrel turned down by a company like Adco isn't that expensive, but the few places that are willing to pull apart an MR556 upper receiver and then turn down the barrel, are quite a bit more expensive. I felt that it was probably worth it to send my stupid-expensive upper to one of these places that had the proper tools to take it apart, but after e-mailing them and specifically asking them if they had the special tools, I got the impression that they did not actually have them. So I thought--screw that. I'm not shelling out a bunch of money for something I should be able to do myself. I was unable to find any definitive information on-line about pulling the barrel, except a little 'This is how you do it--Nuhah, you do it like this' bickering back and forth. So I forged along on my own, determined to succeed, or spend a ton of money breaking something.

    Flash hider removal. I have an aluminum barrel clamp, so this wasn't a big deal. Next up was the barrel nut. First off, one of the only threads I could find about pulling the barrel suggested clamping the barrel in a vise (in a barrel clamp), and turning the barrel nut. I tried this first, using a strap wrnech on the barrel nut, without success. After trying it this way, I am convinced that this is not the way to do it. I really think the proper, and safest way, to do it, is to clamp the receiver in a vice (in a fixture) and loosen the nut...Which is what I did next.

    I used my standard Brownells A2 / A3 plastic upper receiver vise fixture that I already had. However, it did not fit the HK upper properly. It seems as though the HK upper is larger in some areas than a standard AR upper, so I had to break out the dremel and remove some plastic to make the upper fit into the fixture properly. Once I got it to fit properly, I inserted the plastic 'bolt' included in the kit in the receiver (to avoid crushing the upper) and placed it in the vise. Next challenge was the nut. It obviously requires a special spanner wrench, which I didn't have. I did find, however, in a pile of old tools, a spanner wrench with a claw on the end, which appeared to be close in size. I ground down the 'claw' untill I had a round peg, and it fit the barrel nut perfectly.

    So I was now at the point of no return. I was either going to spin the nut off, or break something--as I didn't really know what to expect.

    So a stiff push on the wrench, and nut broke free. That was it. In the end, it comes apart just like any other AR barrel. However, the fit between the barrel extension and receiver extension is MUCH tighter than any AR I have taken apart. Again, I really believe the way to take it apart is to support the receiver with the appropriate fixture, not the barrel. I suspect the barrel will need to be frozen when I re-install it. Also, the roll / split pins that hold the gas block are very tight. I'm not looking forward to putting them back in, if they have 'unrolled' at all. By the way, the barrel has an 'index pin' just like any other AR.

    If anyone is curious, the stripped barrel weighs 2 lbs, 8 oz. I'll let you know how much it weighs when I get it back in a few weeks.

  2. #2
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    thanks for the information. Hopefully someone will offer a dedicated tool to remove the barrell nut here soon.

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    I believe that it has been mentioned that the barrel is frozen or the receiver is heated during installation at the factory. It is supposed to be extremely tight. It's probably not optimum to pry it apart or put it back together using only brute force.
    Do you even HK, Bro?

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    Proper procedure is to use counter bracket for barrel change, that goes inside barrel extension and block it, then unscrew barrel nut.

    BTW Proper torque for reassembly is 110Nm+-10 and mandatory use GO and NO-GO 5.56 gauges after barrel assembly to check headspace.
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    The right tool for the job...



    I'm in Orlando if any MR or 416 owners need help removing their barrels.

  7. #6
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    Quote Originally Posted by dwillHK View Post
    It is supposed to be extremely tight.
    In my experience, that's not the case.

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    Quote Originally Posted by tlrgsxr View Post
    The right tool for the job...



    I'm in Orlando if any MR or 416 owners need help removing their barrels.
    AACK!! Where were you last week!?

    What does the other special tool look like--the one that goes in the upper / chamber area? Are the two pins in your picture punches?

    ETA Oh I see now. The pin goes in the fixture for the barrel nut. That way it doesn't have to be hinged like a spanner wrench. And it captures it on both sides. That's pretty neat.
    Last edited by razzman1; 11-21-2011 at 10:24 AM.

  9. #8
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    Got the barrel back from Adco this afternoon. Re-profiling just the area under the handguard to .700 took about 9 oz out of the barrel. That's not as much as I had hoped for, but exactly what they predicted. We'll see if it makes any noticeable difference in the way it feels. Reassembly starts in a few hours, and I'll post some pics when I'm done.

  10. #9
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    Well, reassembly went smoother than I anticipated. I left the barrel in the freezer for about 7 hours, and right before reassembly, I warmed up the receiver with a heat gun. Both the barrel and the gas block went back on MUCH easier than they came off.

    Pics of the new barrel profile:



    And assembled, ready for a 3-gun match to break out.



    I realize 9 ounces isn't a lot of weight (removed), but I can feel the difference, and I'm glad I had it done.

  11. #10
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    Can I ask you what scope mount is that? thanks. BTW good job!

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