3-lug worth a damn..?

Discussion in 'NFA - Stamp collecting' started by bigfelipe, Apr 12, 2020.

  1. bigfelipe

    bigfelipe Phil-osopher... Charter Life Member

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    Gemtech makes a 3-lug adapter that fits my Thompson Machine ISIS-II. Interested in getting one and some lug mounts for my 300blk AR and Ruger American, so I can switch back and forth faster and easier...


    I've read there can be wobble in them. That concerns me. Been around forever. Am I concerned for nothing? Is it a good retrofit system?
     
  2. MichaelHK

    MichaelHK Happy to be here

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    It really comes down to the tolerances between your specific mount and the barrel. I use 3-lug everything between different brands of mounts/barrels without issue, however I have had an out of spec mount before that wouldn't work on most of my barrels. Sent it back for a new mount and all is well. I would recommend it, but that's just me.
     
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  3. Slacker

    Slacker Liquor and Whores...

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    I'd recommend it for pistol calibers.
    Not on a bolt gun. I also got out of spec issues, no fit. It's not uncommon.
    I have that exact gemtech mount.
    You can check it out on Saturday after cggr.
    Bring yer' host.
     
    Last edited: Apr 12, 2020
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  4. bigfelipe

    bigfelipe Phil-osopher... Charter Life Member

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    I should have just called you, lol...
     
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  5. JRHorne

    JRHorne Certified Hater Supporting Member

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    Have 3 lugs on my Scorpion, 2 AR9 uppers, Zenith MP5 clone, and about to get one for my MPX. All for my Omega 9K with Rugged Obsidian 3-lug mount. No wobble and absolutely love it.

    I love it so much that I am going to build a 9MM Form 1 can with a trilug adapter.
     
  6. Clicker

    Clicker Member

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    Can you even get anything produced by Gemtech now? I tried forever to buy a bushing / piston for my Raptor 40 so I could use it on my MP5/9mm, finally gave up and machined one my self.
    Now as to your question - I have two cans with 3 lug mounts and love them but they're used on subguns.
     
  7. bigfelipe

    bigfelipe Phil-osopher... Charter Life Member

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    Why aren't 3-lug used on rifles? I'm only looking at blackout. So, it's really an intermediate cartridge...
     
  8. bigfelipe

    bigfelipe Phil-osopher... Charter Life Member

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    Gemtech's site is out of stock but several other spots have them in stock and cheaper...
     
  9. JRHorne

    JRHorne Certified Hater Supporting Member

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    As I understand it, 3 lug is good to go on .300 as long as you're shooting subs. Otherwise and for other rifle cartridges, I believe the pressure is too high.
     
    Last edited: Apr 12, 2020
  10. bigfelipe

    bigfelipe Phil-osopher... Charter Life Member

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    Like for real, or rated? I shoot supers through pistol cans that aren't rated for it all the time. Including those cheap Chinese form-1 wix cans. Full power 300blk just isn't that big a charge.
     
  11. JRHorne

    JRHorne Certified Hater Supporting Member

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    I'm speaking from a warranty coverage and don't blow your sh!t up perspective. I'm sure many have done it and it's fine.
     
  12. some_kid6

    some_kid6 New Member

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    3 lug on a rifle caliber gets too hot and anneals the spring according to this demonstration by SilencerCo. Subsonic 300 blk is closer to pistol pressures/temps so it doesn't have the rifle problems. Supersonic 300 blk would have the problem however since it's back to being at rifle pressures/temps
     
  13. MadMardigan

    MadMardigan Antagonist

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    my griffin Optimus 3 lug is good to go on 300blk super and sub, 9” barrel I think for super, and full auto,

    9F00F142-46AC-41C6-9A54-CC0A0B971E73.jpeg
     
    Last edited: Apr 14, 2020
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  14. shadowsbane

    shadowsbane Member

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    3 lug mounts are the best thing to ever come out of hk.
     
  15. wired

    wired Active Member

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    I just got a SDTA 3 lug mount for a form 1 can I'm building on a B tube. Yeah, That was a waste of money. That is the worst silencer mount Ive ever seen. Tried it on 6 different 3 lug barrels and the worst had 1/2" of play at the end of the tube and the best maybe 3/8" .
     
  16. JRHorne

    JRHorne Certified Hater Supporting Member

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    My Rugged Obsidian 3 lug adapter on my Omega 9K has no play. I've got about 500 rounds through it between my Scorpion, Zenith, and AR9. Trilug for my MPX ordered today!
     
  17. wired

    wired Active Member

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    My Tirant's 3 lug is rock solid. Its just stat SD Tactical 3 lug thats a piece of crap.
     
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  18. Clicker

    Clicker Member

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    Have you tried removing the bushing from the mount to check it on the barrel? You might be able to machine a new one and eliminate that play. If it's the lug lock up portion then yeah you're screwed.
     
  19. Slacker

    Slacker Liquor and Whores...

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    I have found a good bit of accuracy problems with my various 3 lug mounts.
    Pistol calibers, not such an issue but I expect more from rifle.
    It's worth noting that high volume shooters will find periodic cleaning of the mount is required.

    Orientation of the mount is important for repeated POA/POI. I use a witness mark to ensure its the same each time. Otherwise, you will go nuts.
     
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  20. wired

    wired Active Member

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    Its the bushing. Its .598" inside which is a good .010" fatter than it should be. Lots of slop. I would never use it as is. I can return it and hope for better or just machine one myself. I'll probably machine one myself.