barrel diameters and muzzle brakes.

[Clark]

It seems there are some standard muzzle threads, but I got a barrel that is odd.... 1/2 -24.

It was read to install but got surplused and I got it for $100. I am putting in on a Mosin Nagant.

I had to make my own thread protector from some hex steel.

 

[bigngreen]

I've been concerned about min thread diameters especially with factory RUM's which seems to be the most popular to brake if you can imagine that.

I talking it over with an engineer who is familiar with what I'm doing and he put together a program for me to just punch in numbers and it tells me where I'm at and gives me a safety factor for that specific case since it changes with bore diameter. He built in some safety by using the numbers for 416 Stainless in an annealed state.
I punched in the a .310 bore with .648 OD and my program tells me it's good to 18,000 psi muzzle pressure with annealed 416, a bare 9/16-28 thread is right at the line with annealed 416, I forget the term he used but that line is just where the metal will start to move but it will spring back and not permanently deform or fail for quite a little more pressure so a 9/16-28 is well within spec and 1/2-28 is good for 13,000 psi on annealed 416. A 4140 barrel steel is good for quite a little more and a 1/2-28 is well within it's operating range on the .310 bore.

 

[hemiford]

How can you calculate the pressure of a 375 RUM at the muzzle,
with 26-in barrel ?

 

[Edd]

How can you calculate the pressure of a 375 RUM at the muzzle,
with 26-in barrel ?

You can't, but you can drill a hole in the barrel and measure it with a transducer.

 

[bigngreen]

Quickload will get you close or I get exit pressure data from a pressure trace system if it is something I can put a sensor on.

 

[hemiford]

Hmmm.
I can't do any measuring. But, with a little reasoning I can predict the
muzzle pressure on the 375 would be less than a 300 RUM because
it has a greater expansion ratio (same barrel length). Offsetting that fact,
however, is that the 375 has a thinner wall thickness at the muzzle,
(both are factory barrels).

 

[Clark]

I have quickload that calculates muzzle pressure.
I can calculate thin wall and thick wall hoop stress in steel.
All this talk about threaded muzzles failing is silly.

 

[J E Custom]

All this talk about threaded muzzles failing is silly.[/QUOTE]



There is nothing Silly about safety in design of a firearm.

Not trying to start an argument but if you think it can't happen you are wrong.

I have re threaded barrels that for one reason or another have shot the brake Off and the owners did not think it was silly at all. fortunately I have not been close to a rifle when this happens, I just
end up fixing the problem after it was created.

Engineers normally design for the worst case scenario.(Plan for the worst and hope for the best)
Long Range hunters are notorious for loading to and above the max in order to get the velocity
for longer shots. So the logic of designing to worst case scenario is what keeps us safe.

I am glad you have not had this problem and hope you never do.

My post was intended to help those that don't know how to calculate all of these variables to come
up with a safe installation, and rely on there smith to keep them from making a poor or unsafe decision.

Sorry I tried to help these folks, but I didn't want them to make the mistakes that others have already made.

I hope this doesn't offend you because that was not the intent.

J E CUSTOM

 

[Clark]

All this talk about threaded muzzles failing is silly.

There is nothing Silly about safety in design of a firearm.

Not trying to start an argument but if you think it can't happen you are wrong.



J E CUSTOM[/QUOTE]

You might calculate that a 30 cal muzzle with 20kpsi needs to have wall thickness of PA/2s = 20kpi [.3/2]^2/2[120k] = .006" thick walls. The peak of the threads helps. Hoop stress is twice longitudinal stress, so where it is threaded, it could be less than .006" thick walls.


It was back in the 1990s that my father, the chief engineer gun designer and a mechanical engineering professor showed me how to calculate hoop stress [and shear stress and section modulus] so I could know how hot I could load a 45/70 handi rifle. I think my calculation shows up on the old usenet for rec.guns.

 

[shortgrass]

There is nothing Silly about safety in design of a firearm.

Not trying to start an argument but if you think it can't happen you are wrong.



J E CUSTOM

You might calculate that a 30 cal muzzle with 20kpsi needs to have wall thickness of PA/2s = 20kpi [.3/2]^2/2[120k] = .006" thick walls. The peak of the threads helps. Hoop stress is twice longitudinal stress, so where it is threaded, it could be less than .006" thick walls.


It was back in the 1990s that my father, the chief engineer gun designer and a mechanical engineering professor showed me how to calculate hoop stress [and shear stress and section modulus] so I could know how hot I could load a 45/70 handi rifle. I think my calculation shows up on the old usenet for rec.guns.[/QUOTE]
I, for one, want wall thickness under the threads to be more than .006"! I don't care whos' calculations came up with that number. That's just plain insane! News print is about .003" thick, copy paper .004".

 

[J E Custom]

I promise, this will be the last post on this subject from me.

It is going no where and lost it's purpose. Use the chart or don't.

I will continue using the chart and will not infringe on the minimum barrel wall thickness.
Even though I added .010 to the minimum, that's not very conservative In my opinion and does not prevent any installations that fall within the recommended thickness.

J E CUSTOM

 

[FEENIX]

I promise, this will be the last post on this subject from me.

It is going no where and lost it's purpose. Use the chart or don't.

I will continue using the chart and will not infringe on the minimum barrel wall thickness.
Even though I added .010 to the minimum, that's not very conservative In my opinion and does not prevent any installations that fall within the recommended thickness.

J E CUSTOM

Please don't stop, most of us value safety.

If people choose to ignore safety concerns; that's their problem.lightbulb

Thanks!

Ed

 

[shortgrass]

There is nothing Silly about safety in design of a firearm.

Not trying to start an argument but if you think it can't happen you are wrong.



J E CUSTOM

You might calculate that a 30 cal muzzle with 20kpsi needs to have wall thickness of PA/2s = 20kpi [.3/2]^2/2[120k] = .006" thick walls. The peak of the threads helps. Hoop stress is twice longitudinal stress, so where it is threaded, it could be less than .006" thick walls.


It was back in the 1990s that my father, the chief engineer gun designer and a mechanical engineering professor showed me how to calculate hoop stress [and shear stress and section modulus] so I could know how hot I could load a 45/70 handi rifle. I think my calculation shows up on the old usenet for rec.guns.[/QUOTE]

Your concerns about your 45/70 cal. Handi-Rifle are completely misguided. That wouldn't be so much about the strength of the barrel, but the strength of the action and its method of locking into battery . It was designed for no more than SAAMI speced ammo. I've seen more than one Handi-Rifle locked-up (unable to open the action) after shooting hot hand loads. Heck, I've one or two that were locked-up (couldn't open the action) after shooting factory loaded ammo.

 

[Clark]

You might calculate that a 30 cal muzzle with 20kpsi needs to have wall thickness of PA/2s = 20kpi [.3/2]^2/2[120k] = .006" thick walls. The peak of the threads helps. Hoop stress is twice longitudinal stress, so where it is threaded, it could be less than .006" thick walls.


It was back in the 1990s that my father, the chief engineer gun designer and a mechanical engineering professor showed me how to calculate hoop stress [and shear stress and section modulus] so I could know how hot I could load a 45/70 handi rifle. I think my calculation shows up on the old usenet for rec.guns.

Your concerns about your 45/70 cal. Handi-Rifle are completely misguided. That wouldn't be so much about the strength of the barrel, but the strength of the action and its method of locking into battery . It was designed for no more than SAAMI speced ammo. I've seen more than one Handi-Rifle locked-up (unable to open the action) after shooting hot hand loads. Heck, I've one or two that were locked-up (couldn't open the action) after shooting factory loaded ammo.

It is getting harder to find the old internet, but here is an artifact
https://groups.google.com/forum/#!msg/rec.guns/yGNAQRhJLVA/R7MsDyb-S64J

I had a lot of complaints that posters did not believe the handi rifle was a strong as I said it was, so I did an overload work up to verify it.

Here is my test data:
45/70 work up with; 405 gr cast with lube bands, CCI 200 primers, Win
brass, old Unique [dirty] powder, chamber well lubricated between
firings with CLP for max bolt thrust.

Quickload calculation of pressure and velocity with 405 gr, Unique

shot 1) 18 gr, 33,217psi, 1403 fps, primer looks fine.
shot 2) 20 gr, 39,435 psi, 1485 fps, primer is fine
shot 3) 22 gr, 46,133 psi, 1563 fps, primer looks flat.
shot 4) 24 gr, 53,334 psi, 1637 fps, primer is flat.
shot 5) 26 gr, 61,067 psi, 1709 fps, primer is top hat and flowing,
action popped open and case ejected on firing
shot 6) 28 gr, 69,366 psi, 1778 fps, primer is top hat and flowing, case
head expansion .001", action popped open and case ejected on firing
shot 7) 30 gr, 78275 psi, 1846 fsp, case head expansion .0015" action
popped open and case ejected on firing, some leading in the muzzle.
shot 8) 32 gr, 87,841 psi, 1911 fps, case head expansion .0025", case head separating where case head is flowing into the extractor, action popped open, some leading in the muzzle, and case ejected on firing, primer is spreading out .010"

There was no change in headspace, but I had to stop the work up because of case head separation where the case head flowed into the extractor.

Years later Marlin bought NEF and H&R and answered the question, "Is the 45/70 handi rifle a the trapdoor level, the lever action level, or the Ruger #1 level?"

Marlin answered that the 45/70 handi rifle is at the lever action level of pressure capability.

What does it all mean?
My Handi rifle math was not convincing.
My handi rifle test data was not convincing.