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Rifles, Reloading, Optics, Equipment
Gunsmithing
Muzzle break threading 300 win mag
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<blockquote data-quote="J E Custom" data-source="post: 1312019" data-attributes="member: 2736"><p>Just a word of caution. when I started making custom brakes I was curious about minimum safe wall thickness of barrels after threading, and talked to many barrel makers and there engineers,</p><p></p><p>The numbers varied from .137 thousandths to .150 thousandths Safe minimum at the muzzle.</p><p>(.013 thousandths difference between all of there recommendations).</p><p></p><p>If you look at a 1/2" 28 thread on a .308, this is what you have for a wall thickness.</p><p></p><p>Minor diameter of a 1/2 28 thread is .0219 + or - depending on the quality of the threads</p><p>- .500 major diameter of 1/2 '' 28 = .486 minus the .308 bore diameter = .181 divided by</p><p>2 equals .090 wall thickness. (Almost 1/2 of the recommended wall thickness).</p><p></p><p>Comments:</p><p>There is normally .002 thousandths clearance between the major diameter of threads and the minor</p><p>diameter in order to fit properly. So I don't want to rely on the brake to support the barrel threads.</p><p>many thread fits are much worse than that But even if we assume they are the best it still does not</p><p>truly support the barrel threads unless you use some kind of thread filler that hardens to fill the space in the threads.</p><p></p><p>Most manufactures have gone to 5/8 24 threads for .308 bores and feel it is a safe thread diameter.</p><p>It also helps to prevent the phenomena of bore diameter changes when tightening the brake. </p><p></p><p>lots of older rifles and ultra light rifles have barrels that were never intended for brakes and the barrels are to small for a threaded brake. this is case for the clamp on brakes to be used.</p><p></p><p>I have seen brakes shot off the barrel and have repaired some of them and in many cases the person or smith could have used a larger thread diameter.</p><p></p><p>I can only warn people that just because it has been done, doesn't mean it is safe because there are so many variables. </p><p></p><p>So, If a person can live with a wall thickness of .090 thousandths, then the 1/2'' threads on a .308</p><p>may be ok as long as everything is good and the barrel material will support this wall thickness, but I will not depend on it and prefer to go by the recommendations of people that build barrels and know the material strength.</p><p></p><p>This is just My opinion and not intended to start an argument.</p><p></p><p>J E CUSTOM</p></blockquote><p></p>
[QUOTE="J E Custom, post: 1312019, member: 2736"] Just a word of caution. when I started making custom brakes I was curious about minimum safe wall thickness of barrels after threading, and talked to many barrel makers and there engineers, The numbers varied from .137 thousandths to .150 thousandths Safe minimum at the muzzle. (.013 thousandths difference between all of there recommendations). If you look at a 1/2" 28 thread on a .308, this is what you have for a wall thickness. Minor diameter of a 1/2 28 thread is .0219 + or - depending on the quality of the threads - .500 major diameter of 1/2 '' 28 = .486 minus the .308 bore diameter = .181 divided by 2 equals .090 wall thickness. (Almost 1/2 of the recommended wall thickness). Comments: There is normally .002 thousandths clearance between the major diameter of threads and the minor diameter in order to fit properly. So I don't want to rely on the brake to support the barrel threads. many thread fits are much worse than that But even if we assume they are the best it still does not truly support the barrel threads unless you use some kind of thread filler that hardens to fill the space in the threads. Most manufactures have gone to 5/8 24 threads for .308 bores and feel it is a safe thread diameter. It also helps to prevent the phenomena of bore diameter changes when tightening the brake. lots of older rifles and ultra light rifles have barrels that were never intended for brakes and the barrels are to small for a threaded brake. this is case for the clamp on brakes to be used. I have seen brakes shot off the barrel and have repaired some of them and in many cases the person or smith could have used a larger thread diameter. I can only warn people that just because it has been done, doesn't mean it is safe because there are so many variables. So, If a person can live with a wall thickness of .090 thousandths, then the 1/2'' threads on a .308 may be ok as long as everything is good and the barrel material will support this wall thickness, but I will not depend on it and prefer to go by the recommendations of people that build barrels and know the material strength. This is just My opinion and not intended to start an argument. J E CUSTOM [/QUOTE]
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