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Threading a barrel

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Unread 09-20-2012, 12:33 PM
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Join Date: Jun 2012
Location: Minnesota
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Threading a barrel

I would like to make and install my own muzzel break. I am a machinest but have little knowledge of gunsmithing. My main question is what size thread, how many threads per inch? And how much larger should the hole the bullet passes thru on the break be than the bullet itself. Also what kind of work holding is used to thread the barrel, should i make tappered jaws for my lathe or is there a different way? Any advice would be greatly apperciated?
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    Unread 09-20-2012, 02:08 PM
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    Join Date: Oct 2008
    Location: Boise, ID
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    Re: Threading a barrel

    The thread pitch typically runs 24 to 32 with muzzle brakes. If your making your own pick a pitch. The diameter of the threads depends on bore size and barrel OD. I try to use the largest thread size I can to keep the barrel walls as thick as I can. There is less chance of distorting the bore when the brake is tightened that way. I usually run .015 to .020 over bullet diameter.
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    Unread 09-20-2012, 04:42 PM
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    Join Date: Mar 2012
    Posts: 226
    Re: Threading a barrel

    i've seen some use thin aluminum strips on the jaws with a spider to protect the barrel and ive seen some actually make fixtures that have bolts with brass tips on 4 sides allowing you to get it concentric with a contoured barrel while protecting finish with brass tips. some will open up the muzzle up to .030 id go with .020

    Last edited by lightflight; 09-20-2012 at 04:44 PM. Reason: spelling
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    Unread 09-20-2012, 06:14 PM
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    Join Date: Sep 2012
    Location: Wenatchee WA
    Posts: 1
    Re: Threading a barrel

    Depending on the length of your barrel / lathe set up you can either run it between centers, which requires re crowning after, or like most people you can just use a four jaw chuck are run the barrel threw and use a spider with brass tipped screws to center the rear portion of the barrel. I put aluminum material on the jaws to prevent marring the finish. Center off the bore and it seems more muzzle brakes recommend .020" over bore diameter.
    Hope this Helps
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    Unread 09-20-2012, 09:03 PM
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    Join Date: Jun 2004
    Location: Texas
    Posts: 1,074
    Re: Threading a barrel

    I pretty much agree with all the replies. I'm not a skilled machinist, and internal threads are a little more tricky for me, but I have made several muzzle brakes and flash suppressors and I like 24 tpi for muzzle tenon threads over 5/8", and 28 tpi for all smaller diameters. My lathe won't cut a 32 tpi, but if it would, I'd use that pitch on 1/2" tenons and smaller. It's easier for me to thread the brake first and then cut the barrel tenon thread to fit it. Also, if the brake has to be timed on the barrel, the tenon shoulder and tenon length are easier to adjust, and you're already set up to crown the muzzle when you finish the brake installation. I only do single-point crowns with no chamfers.

    1/2" 28 tpi is the standard pitch for AR-15 brakes, flash suppressors, etc.

    On the setup, I usually set up (if the barrel is long enough) with a spider on the back of the spindle, and brass shimstock around the barrel to prevent the jaw faces from marking the barrel (tapered or straight). Doesn't take a whole lot to hold the barrel for me. I stick just enough of the barrel out of the jaws to clear the tools and tool holders, and I take very shallow cuts while turning and threading, and keep track of where my compound is on the feed dial. I always start at zero on the compound and zero on the crossfeed, stop a lot to try the thread fit, and then record where the compound feed dial is when the thread fit is made. I really like the feel of a well-fitted fine thread.

    It's good to use a range rod to perfectly center the bore in the chuck, and it's good to use a tiny boring bar to finish the baffle and exit holes. I use a minimum of .020" and am comfortable with .030" over bullet diameter. Some recommend only .010 over bullet diameter, but I believe it adversely affects accuracy, and doesn't improve brake performance.

    If you have a "Super Spacer" for your mill, it is great for making your own brakes.

    Since Im not a skilled machinist, I can only relate the things I've learned that work for me. Just my opinion, based on some experience. Gun work is not rocket science, just sound planning, meticulous workmanship, precision fits, and no "close enoughs".

    Enjoy, Tom
    Texas State Rifle Association Life Member
    NRA Endowment Life Member

    A big fast bullet will beat a little fast bullet every time
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    Unread 09-21-2012, 03:21 PM
    Silver Member
    Join Date: Jan 2011
    Location: Deep South Texas
    Posts: 106
    Re: Threading a barrel

    Here is a thread by Lorenzo (Grit) on his process of installing a muzzle brake. Muzzle brakes that don't blow off
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