I am not an expert or a lawyer but I think they are only liable if they threaded it themselves. If you have it done elsewhere, then I do not think they are liable.
Last edited:
Barrel too small for 1/2" threadding?
- Thread starter cohunt
- Start date
Help Support Long Range Hunting Forum
I am not an expert or a lawyer but I think they are only liable if they threaded it themselves. If you have it done elsewhere, then I do not think they are liable.
cohunt
Well-Known Member
I'm not threading a kimber, they come from the factory that way
LOL, I was not certain which is the case that is why I responded as such. In either case my response is probably an accurate statement
...
Last edited:
J E Custom
Well-Known Member
I went back through my metallurgical hand books and my engineering books to see if I could find any reference to barrel diameter needed and tensile strength (To old to remember all of this stuff) and this is what I found.
The tensile strength of 4140 barrel steel is 125,000 psi.
The minimum SAMMI pressure for a 308 is 50,000 psi and the maximum SAMMI pressure is 60,200 PSI so the minimum barrel wall thickness based off tensile strength and pressure requirements for a 308 the minimum wall thickness is .123.2 thousandths at 50,000 psi and .148.5 at 60,200 PSI
This requires that the minimum barrel diameter is .554.4 thousandths.
So this means that a 1/2" thread should never be used on a ,308 diameter bore. This is SAMMI specifications and they allow for a safety margin. Anything less and you are removing the safety margin. And if you load hotter than SAMMI recommendations (Which we often do) You risk catastrophic failure and when installing a muzzle brake, you can see why I liked the .150 Minimum wall thickness IT is only .0015 above the recommended SAMMI thickness (I Am known to be Conservative but not very much in this case).
These dimensions are for a plain barrel and do not take in account a muzzle brake install with all of its possible faults if not installed correctly.
Oh Well, at least I got to work that one remaining gray cell a little bit
J E CUSTOM
The tensile strength of 4140 barrel steel is 125,000 psi.
The minimum SAMMI pressure for a 308 is 50,000 psi and the maximum SAMMI pressure is 60,200 PSI so the minimum barrel wall thickness based off tensile strength and pressure requirements for a 308 the minimum wall thickness is .123.2 thousandths at 50,000 psi and .148.5 at 60,200 PSI
This requires that the minimum barrel diameter is .554.4 thousandths.
So this means that a 1/2" thread should never be used on a ,308 diameter bore. This is SAMMI specifications and they allow for a safety margin. Anything less and you are removing the safety margin. And if you load hotter than SAMMI recommendations (Which we often do) You risk catastrophic failure and when installing a muzzle brake, you can see why I liked the .150 Minimum wall thickness IT is only .0015 above the recommended SAMMI thickness (I Am known to be Conservative but not very much in this case).
These dimensions are for a plain barrel and do not take in account a muzzle brake install with all of its possible faults if not installed correctly.
Oh Well, at least I got to work that one remaining gray cell a little bit
J E CUSTOM
J E Custom
Well-Known Member
That's what I enjoy about this site, It forces us Old guy's to bring up things of olden days and learn new things that we wish we had 50 years ago.
J E CUSTOM
cohunt
Well-Known Member
I went back through my metallurgical hand books and my engineering books to see if I could find any reference to barrel diameter needed and tensile strength (To old to remember all of this stuff) and this is what I found.
The tensile strength of 4140 barrel steel is 125,000 psi.
The minimum SAMMI pressure for a 308 is 50,000 psi and the maximum SAMMI pressure is 60,200 PSI so the minimum barrel wall thickness based off tensile strength and pressure requirements for a 308 the minimum wall thickness is .123.2 thousandths at 50,000 psi and .148.5 at 60,200 PSI
This requires that the minimum barrel diameter is .554.4 thousandths.
So this means that a 1/2" thread should never be used on a ,308 diameter bore. This is SAMMI specifications and they allow for a safety margin. Anything less and you are removing the safety margin. And if you load hotter than SAMMI recommendations (Which we often do) You risk catastrophic failure and when installing a muzzle brake, you can see why I liked the .150 Minimum wall thickness IT is only .0015 above the recommended SAMMI thickness (I Am known to be Conservative but not very much in this case).
These dimensions are for a plain barrel and do not take in account a muzzle brake install with all of its possible faults if not installed correctly.
Oh Well, at least I got to work that one remaining gray cell a little bit
J E CUSTOM
Just for fun, does it say anything about diameter in relation to barrel length? 50-60kpsi would be max pressure right? I know pressure drops fairly fast so theoretically the muzzle needs much less than just after the chamber
At 20" a 223 has dropped to just about 10000psi, 1/5th of the pressure peak (pressure peak in a 223 is at about 3 1/2" after that pressure starts to drop.
What is the tinsel strength of SS?
Wouldn't this be a hoop stress calculation, not tinsel strength?
Say you have a 308 or 7mm08 with a muzzle diameter of 0.60". If the recommended min barrel diameter for 9/16x24 thread is 0.625, why wouldn't a 1/2x28 thread work?
cohunt
Well-Known Member
It comes down to strength of the barrel, when you take 7/16" --.4375" ( which is actually the outside of the threads not inside /minor thread diam) then subtract the groove diameter of .308 it equals .1295-- then devide it by 2 (as the barrel has 2 sides to it) --- that equals .06475
Some people think this is too thin for safety to contain the pressures of the caliber/cartridge. 308 runs anywhere from 50000-65000 depending on cartridge--- but as I stated about that is peak pressure (which occurs about 3/4" down the barrel, not at the muzzle.
But- it has been proven that small thread diameters can make the inside of the bore diameter smaller from machining, and the outside of the muzzle can swell from pressure.
I would love to see documented data on the kimber mountain ascent rifles in 300wsm and 300wm as they use 7/16" threads, I have not heard of any issues-sans some accuracy problems- which I wonder if they are muzzle swelling related, or lightweight rifle issues, I hear they can have other issues like mag box bind and finicky on action screw torque also.
All in all it's kind of like barrel break in and cleaning topics.
My question wasnt about the bore diameter vs thread diameter as I know it's a "touchy" subject--- it was more about if there would be enough of a shoulder to properly mount a muzzle brake on-- not even a suppressor as i know that's a whole other topic also.
I have a .650" barrel threaded for 9/16 so that would make me think a .555" barrel would be ok for 1/2" threadding -- my local smith told me it had to be 7/16" so I was trying to figure out why.
Last edited:
A.555 outside dia. is only .055 over 1/2 " so to keep it from having to tight of threads it needs turned to .500 then you cut your threads to depth , according to the number of threads per inch how deep . If you are running a .224 bullet you have .331 - half for .1655 barrel meat per side for thread depth before you cut through to the bore . If I was to be ask to cut those threads I would tell you no for my peace of mind that I wasn't going to get you hurt . If you wanted to thread something up against as a stop and to bind it on against a shoulder that would give you a shoulder of .0255 so you would be better off not using a shoulder but using the end of the barrel to butt up against so you really wouldn't have enough of a shoulder . running that small of a barrel I'm not sure why one might want a brake but that's just me . If you had to have a shoulder to time the brake that would be why he wanted to do 7/16 so he could have a shoulder but then he could make some measurements and time it off of the muzzle just as easy as a shoulder.
J E Custom
Well-Known Member
Unfortunately, some people buy a light weight barreled rifle because they want the rifle as light as possible. The down side of this is recoil
due to the light weight and then they decide to go with a muzzle brake to tame the recoil, or load up the but stock with weight (Which defeats the original reason for buying a light weight rifle. Most light weight rifles come with small contours two small to safely install a threaded brake.
I hate the looks of the clamp on brakes, but they are an option to prevent weakening the muzzle for light weight barrels. I have also seen a few of these light barrels split from the muzzle end that apparently was not restricted and split along the rifling. The typical muzzle pressure is 18,000 to 22,000 PSI unless you are using a slow burning powder that cant be consumed by the cartridge/ barrel combination producing more pressure at the muzzle. when a fire ball comes from the muzzle, this normally means that all of the powder is not burned in the barrel and pressures can be higher at the muzzle.
Also most light weight barrels were not designed for a muzzle brake and have just enough barrel wall for the cartridge used.
J E CUSTOM
due to the light weight and then they decide to go with a muzzle brake to tame the recoil, or load up the but stock with weight (Which defeats the original reason for buying a light weight rifle. Most light weight rifles come with small contours two small to safely install a threaded brake.
I hate the looks of the clamp on brakes, but they are an option to prevent weakening the muzzle for light weight barrels. I have also seen a few of these light barrels split from the muzzle end that apparently was not restricted and split along the rifling. The typical muzzle pressure is 18,000 to 22,000 PSI unless you are using a slow burning powder that cant be consumed by the cartridge/ barrel combination producing more pressure at the muzzle. when a fire ball comes from the muzzle, this normally means that all of the powder is not burned in the barrel and pressures can be higher at the muzzle.
Also most light weight barrels were not designed for a muzzle brake and have just enough barrel wall for the cartridge used.
J E CUSTOM
cohunt
Well-Known Member
one more factory rifle to consider now besides the kimbers-- the new weatherby V back-country has a #1 modified profile barrel and its fully fluted too--not sure what thread size it will have as it is not announced yet, but I'm guessing it could be 7/16" due to that #1 profile barrel-- they sell it in 300WM
John Klingenberg
Well-Known Member
Use a jam nut to create a false shoulder. Make sure your gunsmith can cut the thread on a lathe or mill in small passes instead of using a die (eye roll) which could constrict the muzzle. They can cut it with a max spec outside and have a very snug fit but it gives you a margin. If you have such a thin barrel wall Id be hesitant to butt up against the muzzle. Unless the internals of the brake were very precise you'd have a very small contact area. The work you need done has to be done with attention to detail and you'll not have a problem with that project.
