Machining a barrel thread adapter
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  1. #1
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    Default Machining a barrel thread adapter

    I want to machine an adapter that screws onto a metric m14 barrel that has M15x0.75 pitch external threads, to convert to 5/8 for more standard muzzle brakes. Concentricity and alignment are going to be critical. Here is my tentative plan:

    1. Drill and tap for the M15x0.75 and screw adapter onto barrel;
    2. insert a range rod into the barrel through the adapter and true the barrel up with spiders at each end just like chambering through the headstock;
    3. cut and thread the 5/8 tenon with it all aligned;
    4. install the muzzle brake and check for alignment with the range rod, correct by truing up the hole through the brake if necessary.

    Does this sound like an effective way to do this?
    Last edited by Grizzlypeg; 05-15-2019 at 04:48 PM.

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    Quote Originally Posted by Grizzlypeg View Post
    I want to machine an adapter that screws onto a metric m14 barrel that has M15x0.75 pitch external threads, to convert to 5/8 for more standard muzzle brakes.
    You lost me out of the gate. If the barrel is threaded M14 (like an AK, or SKS) where is the M15 coming into the equation?

    Is this what you're looking for?

    M14x1 RH to 5/8-24 RH Thread Adapter

    Reamers follow the existing hole in the brake. When I retrofit, I never bother dialing in precisely because I don't believe a few tenths- or even a thou or two- makes any difference at all. I put the brake in my Buck 6 jaw and ream it to size with a floating reamer holder. A quality brake will have it's hole perfectly concentric to the threads and I'm perfectly content to allow the reamer to follow the hole.

    If it's a new barrel, and it's been dialed in to cut the crown, then I'll bore the brake in-place after threading the muzzle without disturbing the setup.

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    bet he has a Norinco M14...

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    Yes, it is a Norinco M14 with metric thread. The barrel is threaded M15x0.75 for the flash suppressor nut. That thread can also be used to attach a muzzle brake. I want to make an adapter that screws over the (M15x0.75)threaded end of the barrel and terminates in 5/8-24. I'm just mulling over how best to machine it accurately for alignment with the bore. I'm thinking it should be done similar to setup for reaming a chamber, in that I need the external threads I generate on the adapter to be accurate to the bore, just like the shank on a barrel.

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    Have you done the math for this? M15 is nominally .590" and 5/8 is .625". that gives you .035"/2 = .0175" thickness in which to cut the 24 TPI threads. Looks like the minor diameter of 5-8-24 is .574-.575". I don't think a sleeve will work; the threads would have to be one in front of the other.

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    Yes, definitely the threads cannot be on top of each other. Wish I had an easy way to post up a drawing. I envisage a section that goes over the barrel, and a 5/8 threaded portion forward of the barrel.

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    Have you considered *trying* a .595"-32 brake??? It's so close it may be a non issue?

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    I used to make blank muzzle breaks. One of the sizes we made was 1/2-28. If you bought one of these you should be able to bore it out and thread it .590-32, which is pretty close if you do not have metric threading gears.

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    If you’re testing a bunch of 5/8 brakes or other muzzle devices then why not. But if it’s a dedicated brake I think FredC has the right approach.

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    Makes sense about the one off vs trying various brakes. I am mostly doing this for the fun of it, and would like to do it the more complicated way of making an adapter. I can buy a brake that just screws on, but its more fun to do something myself and learn in the process. I have ordered a tap in M15x0.75, and the external 5/8 thread I can cut on my lathe.

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    Well...if ya want the practice, sure.

    But for $35....

    M15x1 RH to 5/8-24 RH Thread Adapter

    For best appearance, buy a round 5/8" brake with an OD slightly larger than the OD of your adapter, screw it on, and turn the OD to "blend" with the adapter. It'll look like one piece when it's done.

    Will that barrel with the front sight fit through your headstock? Gonna be a bitch with that entire barreled action swinging around behind your outboard spider.

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    Quote Originally Posted by tobnpr View Post
    Well...if ya want the practice, sure.

    But for $35....

    M15x1 RH to 5/8-24 RH Thread Adapter

    For best appearance, buy a round 5/8" brake with an OD slightly larger than the OD of your adapter, screw it on, and turn the OD to "blend" with the adapter. It'll look like one piece when it's done.

    Will that barrel with the front sight fit through your headstock? Gonna be a bitch with that entire barreled action swinging around behind your outboard spider.
    Too bad its the wrong thread. The M14S from Norinco uses M15 x .75 threads.

    I can remove the barrel for the job, and the front sights are on the flash suppressor that will have to come off to be replaced with the brake.

    I would like the practice. Making stuff is part of the hobby. It would be far cheaper for me to get someone else to chamber my barrels than me buying a lathe, all those measuring tools, tooling for the lathe, reamers, etc. But, for me, its what I want to do with my spare time.

    I like your idea of blending the adapter and brake. That will make it look pro.

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    Quote Originally Posted by Grizzlypeg View Post
    Too bad its the wrong thread. The M14S from Norinco uses M15 x .75 threads.

    I can remove the barrel for the job, and the front sights are on the flash suppressor that will have to come off to be replaced with the brake.

    I would like the practice. Making stuff is part of the hobby. It would be far cheaper for me to get someone else to chamber my barrels than me buying a lathe, all those measuring tools, tooling for the lathe, reamers, etc. But, for me, its what I want to do with my spare time.

    I like your idea of blending the adapter and brake. That will make it look pro.
    Post up some pics as you progress. Interesting project...good luck with it!

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    Attached to a barrel stub from a metric M14. I am going to make another with more pleasing dimensions, but this is my first one.


    img_1205.jpgimg_1206.jpg

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    Might be the angle of the pictures, but it looks as though neither the brake nor the adapter have flat, square shoulders seating them to the adapter and barrel face?

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    The barrel I believe has to seal to the adapter internally, by having its nose seal up against the inner surface of the adapter. At least that's the way it works with an M14 flash suppressor. The tip of an M14 barrel is made with a reduced diameter and appears to seal by having its crown press against the flat internal surface of the flash suppressor. So, I believe, as it can't seal externally as it has splines on the external surface.

    As for the brake to adapter, is it wrong to rely on the threads forming the seal? I'm speculating here, as it came with both crush washers and a nut. I can see the crush washer sealing as it comes up against a flat shoulder. Not sure about how it is intended to work when you use a nut.

    I'm all ears. This is just a first off. Happy to hear any suggestions.
    Last edited by Grizzlypeg; 06-19-2019 at 02:00 PM.

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    Another option would be to turn down the end of the barrel, removing the M15x0.75 threads. Then turn a sleeve of a good steel, maybe 4140, and do a heat-shrink onto the now-reduced end of the barrel. True it up and then cut your 5/8 threads. Or you could silver solder the sleeve in place, then true it up, and cut threads.

    The only downside is then you're no longer able to mount the stock parts back on the muzzle, but you didn't say that was a requirement.

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    That's a good suggestion. I've turned them down to 1/2-28 and used a brake designed for a 223, having reamed it out for 308 clearance. That worked very well, but its a one way trip for that barrel. The factory flash suppressor that is retained by a castle nut, also contains the iron sights, which are something I would not want to permanently deprive the gun of, in all cases. That's why I'm experimenting around with alternatives.

    You can buy a splined 5/8 adapter that goes in place of the flash suppressor, and is retained by the castle nut, but I'm having fun doing things differently. I have a lathe, so why not play with it?

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    Gotcha... yeah, in that case, your long adapter makes sense. should be simple enough, and like you said, you have a lathe, so why not? Good luck!

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    I have some stainless and some 1045 steel coming to work on the next version. Some of the things I'm learning by doing, and don't have the experience to anticipate all issues, or plan them out ahead of time. This prototype will work, but I know I can do better, and the second version will take only a fraction of the time the first one did.

    I couldn't find any chart that showed what size hole to drill to tap 15mmx0.75. Somehow I made the mistake and ordered a 13.5mm drill. Nope, not even close. So I did the math of major diameter - pitch and came up with 14.25, in inches that's .561. Hey, that's a 9/16 drill bit!!


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