Loose Threads Solved

Gtummy

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Feb 16, 2014
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Beaumont, Texas
This is actually an extension of a post I made from a week ago but information, I think, is important enough I wanted more people to read it. Basic story I had, new to me gunsmith, install a QD muzzle brake on my HK MR762. He commented that I needed to check suppressor alignment, when I got it, because threads felt "Loose". I asked here about the term. Turns out that loose is putting American threaded brake on metric threads. The pitch is the same (standard) but metric cut threads are approximately .03 inches shorter. This was discovered when the recoil of the fourth round fired out of my weapon threw the brake 40 yards out into the range at a 20 degree angle. There was, luckily, no bullet strike. Discovered when 5th shot was a super flyer. Article by Silencer Shop, https://www.silencershop.com/blog/p... of the thread location,a 1/2x20 thread pitch, lists some of the firearms that have this issue.
 
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Zak Smith

TBAC Guy
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The pitch is the same (standard) but metric cut threads are approximately .03 inches shorter.
MR762 is M15x1. 5/8-24 is the American standard for 308. Thread diameter is different (one is "shorter" as you say). The pitch is also different-- 25.4 TPI vs 24 TPI. It would take a very ignorant gunsmith to try to fit one on the other. It'd be like shooting 6.5x47 from a 308 and saying that the rifle is "inaccurate."
 

RonA

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Jul 10, 2011
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MR762 is M15x1. 5/8-24 is the American standard for 308. Thread diameter is different (one is "shorter" as you say). The pitch is also different-- 25.4 TPI vs 24 TPI. It would take a very ignorant gunsmith to try to fit one on the other. It'd be like shooting 6.5x47 from a 308 and saying that the rifle is "inaccurate."
Gunsmith is a very loose term. Metal butcher might be more appropriate. Anyone that would screw a 5/8-24 brake on to
a 15mm thread is too stupid to be allowed to own or work on firearms.
 

nikonNUT

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  • Oct 6, 2019
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    Step 1 when threading; Confirm thread you need. He missed that step.
    It is very possible that he worked in my shop (Hydraulics) for a time. I get that shit all the time :mad: Machinist : "I've taken these 1 1/2-12 threads way below the minor and I can't get this nut to screw down..." Me : "What is the diameter of the rod?" Machinst : "Uhm, 50 millimeter." Me : "So it's a metric rod. Did it occur to you that the threads might be METRIC?!? Try M38x2.0" Machinist : "Oh..." And this is a real person that has "30 years" of machining experience. I hate my job...
     
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    bohem

    PVA's HMFIC
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    Jan 6, 2009
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    www.patriotvalleyarms.com
    It is very possible that he worked in my shop (Hydraulics) for a time. I get that shit all the time :mad: Machinist : "I've taken these 1 1/2-12 threads way below the minor and I can't get this nut to screw down..." Me : "What is the diameter of the rod?" Machinst : "Uhm, 50 millimeter." Me : "So it's a metric rod. Did it occur to you that the threads might be METRIC?!? Try M38x2.0" Machinist : "Oh..." And this is a real person that has "30 years" of machining experience. I hate my job...
    Those are usually the guys who have 8 hours worth of bullshit to sling about "dumb engineers" too.
     
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