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GUNSMITHING SERVICES: Muzzle Threading AND Crowning service

  • $ 10000

The incredible surge in the popularity of suppressors makes a threaded muzzle virtually standard equipment on today's precision rifle.  LRI is well equipped for this extremely popular upgrade.  With our resources and experience, your device will attach trouble free every time.

Muzzle threads for devices like suppressors and brakes are qualified using traceable, certified hard chromed ring gauges or a precision thread pitch micrometer to ensure your accessories adapt without issue.  As standard equipment, we fit these types of muzzles with an 11* target style crown because if machined for the recessed type, carbon deposits faster on the face.

 LRI is vetted and endorsed by ThunderBeast, SRT, and Mac Bros. for suppressor related barrel work. Since the day we've opened, not one of our clients has ever suffered a baffle strike on any muzzle device.


Thompson Center Break Action Rifles:

These types of guns present a unique challenge to gunsmiths performing this service.  The breach end of the barrel has a block welded to it, requiring one of two things:  Either a lathe with a very, very short spindle bore or one with a huge inside diameter.

Because of this very few shops have the ability to thread the muzzle of the barrel.   LRI solved this in a unique way.   We use our industry exclusive 5 axis mill!  Doing so eliminates the complications of setting up the part through the spindle bore of the lathe.  With the use of Renishaw electronic probing, we can position the bore "plumb" to the spindle and locate the center.

From here, it's simple.   We contour the end of the barrel, relieve the bottom at the shoulder, and chamfer the lead where the threads will start.  Then the cylinder portion is threaded using what's called "single point thread milling."   A tool shaped like a saw blade and ground to the shape of a thread form is loaded and it winds down the outside of the cylinder like a spiral staircase.   Very, very accurate threading can be done this way.   The threads are then gauged to ensure they meet the standard afterward.


Important Notes:

First, LRI is not a suppressor manufacturer or retailer.  For specific product information you will have to consult with a dealer/manufacturer.  You need to know exactly what thread diameter and pitch your suppressor is.  LRI does not profess to know the intimate details of ever single suppressor made.  When it comes to suppressors it is literally "the wild west" as it pertains to design and configuration.  There is no "standard".  

It is your responsibility to know exactly what the thread specifications are for the device you are wanting to use. This is very detail oriented because it has to be.  Ensure that you KNOW what the dimensions are.  

Diameter, Pitch, and Class of Thread are what we need to know.


The surge in suppressor use results in us being routinely called to thread muzzles on a variety of rifles.  It's important to understand the limitations we as gunmakers are faced with.  

"Cans" are expensive and anyone who owns one identifies with the administrative gauntlet one has to endure in order to legally own and use it.  The last thing anyone here at LRI wants is to ruin your suppressor due to a machining/installation mistake.

The thread shoulder on the barrel that a suppressor squares up against is an important feature that should be respected for direct mount type cans.  As a cardinal rule we require a minimum of .100" diameter increase over the major diameter of the threads.  


  • 1/2-28 = .600" Shoulder Dia.
  • 9/16-24 = .6625" Shoulder Dia.
  • 5/8-24 = .725" Shoulder Dia.
  • 3/4-24 = .850" Shoulder Dia.
  • M18x1 = .810" Shoulder Dia.
  • "CUSTOM" = +.100" Shoulder Dia. over Major Thread Outside Diameter.

We advise clients to also develop the habit of lubricating threads with a high temperature copper based anti seize compound. -ESPECIALLY with semiautomatic rifles as the heat generated from high volume, sustained shooting can quite literally weld the can to the muzzle!

For heavier varmint/tactical type barrel contours these values are essentially meaningless because the barrels are already significantly larger.  

The slimmer sporter/hunting contour barrels are where the issue becomes very relevant.   We do not keep records on every single sporter barrel contour available from every manufacturer.  You will have to do some research on your end to make sure your barrel can be safely threaded for a suppressor at the finish length you are requesting.

When using a Bartlein #3 contour sporter barrel as an example, the following would apply for approximate barrel lengths that meet the +.100" rule:

  • 1/2-28 = 26" max finish length
  • 9/16-24 = 24.25" max finish length
  • 5/8-24 = 18" max finish length
  • M18x1 = Cannot be used as the barrel will be shorter than the 16" minimum required by law for a non SBR type rifle.

"finish length" is defined as the length of the barrel as it would be sitting on a bench with no receiver attached to it.  The measurement is from breech face to muzzle crown.

Last, the caliber and cartridge for a particular setup must be considered.  As a rule, LRI requires a minimum of .100" of wall thickness between the groove diameter of the barrel and the root diameter of the thread being machined to the muzzle.  This value is judgement based as well.  A 300-378 Weatherby Magnum is a powerful cartridge with muzzle pressures significantly higher than a 308 Winchester at a given barrel length.  Wall thickness should be increased accordingly.

Our experience has shown that a thin wall muzzle has the potential to "bell mouth" over time.  When a crown bell mouths, the accuracy of the rifle suffers.  You as the user may be compelled to think the barrel "let go" due to throat erosion when it's actually because the muzzle was threaded with too thin of a wall thickness.

Please review these notes in detail and fully comprehend what is being explained.  LRI performs this service based on information we receive from you.  We perform the work to established machining practice standards.  

How it gets used is ultimately your decision and responsibility, not ours.

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