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1/2 by 28 thread question

Discussion in 'Gunsmithing - Assembly - Finishing' started by KnotRight, Mar 19, 2020.

  1. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    I was having a problem with my can fitting on one of my guns. So I ordered a tap and die that is 1/2 by 28. The tap says maybe HSS. These are Gravin T&D.

    Is there a difference in 1/2 by 28 threads?
     
  2. ACP

    ACP New Member

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    HSS most likely stands for High Speed Steel in this case
     
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  3. BASIL

    BASIL Member Benefactor Charter Life Member

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    What are you planning to tap? If the can fits all but the one firearm, the problem is with the threads on that gun.
     
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  4. BigWaylon

    BigWaylon Head philatelist Staff Member Benefactor Charter Life Member

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    What can?
    What exactly is the problem?

    Possible the barrel is 1/2-36?
    Possible the threads are too long?
    Might need a 1/2-28 die, not tap, to chase the barrel threads if they’re a little buggered.
     
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  5. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    The guns both have a bird cage or flash hider on them. They both are 1/2 x 28. The end of the can is labeled 1/2 x 28. I was able to put the can on the CMMG without any problems. Then tried to put it on the AR pistol and would not go. On Monday I took the AR-pistol barrel to the local smith and he was able to get a flash hider to start on the barrel but did not screw it all the way down. He did confirm it was a 1/2 x 28. I am going to see it I can swap out the flash hide and bird cages. Here are some pictures of the end of the can, and T & D. I am going to try to run the die down the barrel of the pistol.
    20200319_181315.jpg 20200319_181308.jpg
    20200319_181334.jpg
     
    Last edited: Mar 19, 2020
  6. BowWow

    BowWow Happy to be here

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    For whatever reason, a lot of 9mm ar's are 1/2-36 threads. If the can will not really start....as in you get less than one revolution and it instantly binds up.....its probably not 1/2-28. If it goes on half way or so and is intermittently tight.....the threads on the barrel are probably boogered up. Used the die and some cutting fluid and gently....chase the threads. It shouldnt take a lot of force to chase them. Youtube might have some tips on using dies.
     
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  7. Scsmith42

    Scsmith42 Member Benefactor Charter Life Member

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    There are different classes of thread fits, but most likely your barrel was threaded on a lathe and not by a die. The machinist might have made it a few thousands too large a diameter.

    Most die's are tapered inside, so what you'll need to do is start it normally and run it down until it hits the ledge at the back of the threads, and then remove it, turn it over and very carefully start it again and run it all the way down.

    If your can fits everything else well, I would not run the tap through it mainly because you might increase the hole diameter and have the can loosen up / lose accuracy on your other firearms.
     
  8. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    Pulled the AR-pistol hand-guard off the gun and ran the die over the threads. Had to do it by hand because I did not have a die holder that big. Ran it all the way to the end. Then tried the can, it worked. Put the hand-guard back on and then the can. It looks like the hand-guard is about an 1/16" or less too long. Not sure if the can is resting against the shoulder of the barrel.

    Being new to suppressors, I would think that it is important for the can to tighten up against the shoulder of the barrel. Am I correct?
    Can mounted AR-pistol1.jpg Can mounted AR Pistol2.jpg
     
    Last edited: Mar 19, 2020
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  9. BigWaylon

    BigWaylon Head philatelist Staff Member Benefactor Charter Life Member

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    You want the threads concentric to the bore.
    You want the shoulder square.
    You want the silencer snug against the shoulder.

    That combo is the best way to not have a baffle strike.

    (There are some pistol cans, usually with metric threads, that index off the muzzle instead of the shoulder)
     
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  10. Bailey Boat

    Bailey Boat Senior Member Benefactor Supporting Member

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    There is a HUGE difference between lathe cut threads and die cut threads and you may have just screwed up the pistol by running a common die on the threads. Most dies sold to the public are crap and not worth the steel they waste. You should have taken it to either a gunsmith that's also an accomplished machinist or a qualified machinist for help. Since you can't get the can to seat all the way to the shoulder you have probably guessed which....
     
  11. DrScaryGuy

    DrScaryGuy Well-Known Member

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    yes, get the can snug to the shoulder.
    Rebel just lost their FFL and closed up shop, so don't count on support/repair if you have a baffle strike.
     
  12. Scsmith42

    Scsmith42 Member Benefactor Charter Life Member

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    With all respect, since the threads were originally lathe cut, chasing them with a die should be ok. It will follow the original threads and simply cut them slightly deeper.

    Garvin tooling is out of India and not necessarily what I would consider to be machinist grade tooling though.
     
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  13. Catfish

    Catfish E Pluribus Mendacium Supporting Member

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    Does this mean that you were able to make the can solidly contact the shoulder and that your can is concentric to the bore? Check with a guide rod, available here: https://www.cncwarrior.com/category-s/2086.htm

    You want some clearance between the can and the handguard or accuracy will suffer and you might ding up your can.
    You definitely don't want it to tighten against the handguard.

    It sounds like you have a bad fit to me and you either need to modify your handguard or replace it with one that fits properly.
     
  14. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    @Catfish the rail was about 1/16th of a inch too long. when I screwed the can on without the hand-guard, it bottomed out against the barrel. With the hand-guard, it was bottomed out against the hand-guard. Not sure if I want to find a 7" hand-guard or build an upper that is 8.5" with the hand-rail 7.5 to 8 inches.
     
  15. DickFord

    DickFord Happy to be here

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    A file will fix a 1/16”.


    Sent from my iPhone using Tapatalk
     
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  16. Me.

    Me. Active Member

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    I was thinking a sander or piece of sandpaper flat on a table will take care of that gap in no time.


    It you are a stickler for aesthetics, maybe refinish the end with something better than a Sharpie (which is what I’d use).
     
    Last edited: Mar 25, 2020
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  17. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    When I measured the distance that needed to be sanded, it was a little more than I wanted to do. Now looking for a 8" barrel. Can not believe how hard they are to find without spending a lot of money. More than what I want to spend. Was hoping to keep it around $150. Found one for $87 but not sure I want that in my hand when I pull the trigger.
     
  18. BigWaylon

    BigWaylon Head philatelist Staff Member Benefactor Charter Life Member

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    Caliber? I first thought it was 9mm, but saw the gas block & tube. Is it 5.56?
     
  19. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    This one is a 5.56.
    I ordered a GSL can for the 9. After 10 months of waiting on the Wolfman I gave up.
     
  20. BigWaylon

    BigWaylon Head philatelist Staff Member Benefactor Charter Life Member

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  21. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    Order placed with Opticplanet

    Thanks,
     
    Last edited: Mar 25, 2020
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  22. KnotRight

    KnotRight Well-Known Member Charter Member Benefactor Life Member

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    I got my 8" barrel in yesterday and mounted it today on the AR-pistol. That 1/2 inch made all the difference.
    20200403_144624.jpg 20200403_144630.jpg
     
    Last edited: Apr 3, 2020 at 5:30 PM
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