Muzzle thread size & muzzle swelling?

[DJ Fergus]

http://bulletin.accurateshooter.com/2015/04/muzzle-threading-dont-remove-too-much-steel/
I ran up on this article and was wanting your opinions and if you do think there is some validity to the article, would it apply to button barrels mostly. Thoughts on this article if or if not it would pertain to cut rifle barrels?

 

[L.Sherm]

Why do you think it would only apply to button barrels.

 

[ShtrRdy]

Dang, I never heard of this but it sure seems real by his demonstration.

I wish I had 0.300 +/- gauge pins available to see it I have the problem.

 

[J E Custom]

This has been talked about before but should be again.

There are many things that can cause a diameter change at the muzzle and this is some of them.

1 = insufficient barrel wall thickness.
2 = Improper thread fit between the brake and the barrel tenon.
In my research on minimum wall thickness to manage the pressure at the muzzle, all barrel makers recommended no less than .137 Thousandths + and not being able to rely on thread fit to help. we went to .150 thousandths minimum muzzle wall thickness.

The difference in rifling methods realy make no difference but in reality cut rifle barrels are stress relieved once. buttoned rifled barrels are stressed relieved twice because of the stress inputted during buttoning. so the odds are slightly better that the stress relieve is more consistent with buttoned barrels. but being in the different barrel makers hands we chose not to count on ether method for for the pressure calculations and the best stress relieve for strength.

I always recommend the biggest thread diameter possible, but the minimum wall should never be less that the required thickness. different thread pitches of the same size will add some thickness. If a finer thread is used. (A 32 TPI will have a larger minor diameter that a 24 TPI for the same size thread diameter. but if you calculate the
bore diameter + .150 wall (.300 thousandths total) Example: .308 +
.300 = .608 diameter and as long as the minor diameter of the Thread chosen exceeds this diameter and good threads are cut,you will be good to go.

I have included a link to my web site in the FAQs section that will aid in the selection of thread size minimum, based on barrel size and bore size. (it is in the seventh question)

http://www.jecustom.com/index.php?pg=Home&cmd=Cell&cell=FAQ

For many years the military has used 1/2"x 28 TPI on 556 to .308
in our "opinion" and based on barrel makers recommendations the 1/2 x 28 TPI does not meet the requirements of anything with a bore diameter over.257 and should be avoided if possible.

So to sum it up. take your bore diameter, add .300 to that and if the TPI doesn't infringe on the minimum thickness and you barrel diameter is over the recommended minimum by .050 then subtract the minor diameter of the thread wanted .

J E CUSTOM

 

[DJ Fergus]

Why do you think it would only apply to button barrels.

I wasn't really sure either way if it would make a difference. I also didn't realize that buttoned barrels were stress releived before and also after the buttoning process.

 

[DJ Fergus]

This has been talked about before but should be again.

There are many things that can cause a diameter change at the muzzle and this is some of them.

1 = insufficient barrel wall thickness.
2 = Improper thread fit between the brake and the barrel tenon.
In my research on minimum wall thickness to manage the pressure at the muzzle, all barrel makers recommended no less than .137 Thousandths + and not being able to rely on thread fit to help. we went to .150 thousandths minimum muzzle wall thickness.

The difference in rifling methods realy make no difference but in reality cut rifle barrels are stress relieved once. buttoned rifled barrels are stressed relieved twice because of the stress inputted during buttoning. so the odds are slightly better that the stress relieve is more consistent with buttoned barrels. but being in the different barrel makers hands we chose not to count on ether method for for the pressure calculations and the best stress relieve for strength.

I always recommend the biggest thread diameter possible, but the minimum wall should never be less that the required thickness. different thread pitches of the same size will add some thickness. If a finer thread is used. (A 32 TPI will have a larger minor diameter that a 24 TPI for the same size thread diameter. but if you calculate the
bore diameter + .150 wall (.300 thousandths total) Example: .308 +
.300 = .608 diameter and as long as the minor diameter of the Thread chosen exceeds this diameter and good threads are cut,you will be good to go.

I have included a link to my web site in the FAQs section that will aid in the selection of thread size minimum, based on barrel size and bore size. (it is in the seventh question)

http://www.jecustom.com/index.php?pg=Home&cmd=Cell&cell=FAQ

For many years the military has used 1/2"x 28 TPI on 556 to .308
in our "opinion" and based on barrel makers recommendations the 1/2 x 28 TPI does not meet the requirements of anything with a bore diameter over.257 and should be avoided if possible.

So to sum it up. take your bore diameter, add .300 to that and if the TPI doesn't infringe on the minimum thickness and you barrel diameter is over the recommended minimum by .050 then subtract the minor diameter of the thread wanted .

J E CUSTOM

That clears up alot for me. Thank you for the detailed response. So, it sounds like the industry standard 5/8-24 would be suitable muzzle threads for a large cased 30 cal if the threads are cut correct? I assume 5/8-24 would probably be close to the minimum acceptable on a big 30 cal?

 

[WildBillG]

I am thinking the way you are djfergus. Which would mean my 5/8x24 brake will not work on my 338 project as I had hoped.

 

[J E Custom]

As long as the barrel is over .700 it will meet the minimum requirements but I like .338 barrels to be at least .800 at the muzzle(slightly smaller than a Sendaro contour) so i can use a 11/16 x 24 TPI.

On the 308s the barrel needs to be at least .660 at the muzzle to give you a little shoulder the seat the brake on. On marginal muzzle diameters we like to seat the brake on the muzzle internally instead of the/a shoulder.

I know people like the standard 5/8 x 24 TPI because most or a lot of the suppressors have these threads. But it is always prudent to go with the largest threads that a bore will allow to avoid the less than minimum barrel wall thickness.

J E CUSTOM

 

[WildBillG]

Thanks for that info JE.

 

[DJ Fergus]

Once again, Thank you JE for your in depth response. Folks like yourself are what makes forums like this one great.