AR-15 barrel
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Thread: AR-15 barrel

  1. #1
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    Can anyone advise as to the best lathe speed and type of tool bit for turning down an AR barrel and threading for a muzzle brake?

  2. #2
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    For just turning down area to thread 300 rpm or so, I ground a special 60 degree bit that will clear the shoulder ( small 60 Degree tip with a relief on left edge, 1/4 in HSS tool bit)
    Any HSS toolbits will work just fine, don't need carbide. Threading speed on a normal lathe will be backgear as slow as 50 to 70 RPM only because you have to manually disengage halfnut lever before hitting shoulder. Faster would be better for surface finish, but you would have to have Superhuman timing to prevent a crash. Have done about 50 of these jobs....... Standard AR barrel thread 1/2 x 28 TPI length of thread (including small relief groove at shoulder) to shoulder is .625 .

  3. #3
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    best way to dial it in is a range rod in the bore and a protective plastic sleeve between the 4jaw and the barrel. indicate the od of the range rod ( locked on the id of the barrel lands). The od should be close, but may not be exactly concentric.

  4. #4
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    I turn the muzzle threads With barrel extension/locking lugs in padded 4 Jaw, and bore of muzzle in a long reach CNC type live center to give clearance for 60 degree thread cutting bit. The barrels on ARs are not polished like normal rifle barrels and are more true to ID than a typical spin jig polished barrel blank. And as anyone who has shortened a lot of barrels can state, The middle of the barrel may not be anywhere near concentric with OD........... so a range rod might be pointing off at a several degree angle........ Best to go between centers and kind of average out the error.


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