temperatures effect on everything.

[chkunz]

Ooooh … tay, took awhile but now I get it, I think… Same rate but the diameter change at pick a point on a cylindrical object is greater by 2x the radius the further the check point is from the center point, rite?

One other point, if the barrel is 1.125 inches in diameter in the chamber area, as you assume, a 200 deg temperature rise would result in a 0.0015 inch increase in the external diameter of the barrel in that location due to thermal expansion. This is independent of the chamber or bore dimensions. Probably a realistic increase in temperature rise for an extreme case is less than 200 deg but it gives us a feel for the magnitude of expansion that we are dealing with. Again the important question is what , if anything, does this have to do with accuracy. Take care, Clyde.

 

['Freak]

“Again the important question is what , if anything, does this have to do with accuracy. Take care, Clyde.”

Maybe, a 140°F increase would enlarge a 1.125” CM barrel shank by .001” which could be plenty enough to convince folk having to get off multiple shots within a limited time frame to not epoxy bed anything forward of the recoil lug, and best put that layer of tape on the bottom side of the lug before epoxy bedding. If it’s an 18-8 stainless steel barrel, then it’d take only a 93°F increase to enlarge the stainless shank OD by the same .001”. I’ve seen the harmful effects of trying to bed under the chamber but float the rest.

Internally, the amount of clearance around a bullet’s bearing surface within the throat/leade of a match worthy .30 caliber chamber cut into a stainless barrel could double with a ~ 140°F temperature increase. I can only guess about this one, all mine still have SAAMI chambers where it’d not make a lick of difference.

You take care too,
‘Freak

 

[Canadian bushman]

There are a few small caveats to this.

When a tube cools, the od gets smaller and the id gets larger. The metal reduces area when it contracts. Your bullets are experiencing a similar change.

Also when you look up a coefficient of thermal expansion it is expressed as a change in area per degree, when in actuality the metals expansion and contraction isnt necessarily linear.

Just because when the metal was measured at 20* and 200* and the difference in size was recorded at "X" doesnt mean there wasnt a 40-50* span where it changed significantly less. This is typically why the CTE is presented across different ranges, and always varies.

Just food for thought.

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=M434AE

http://www.matweb.com/search/datasheet.aspx?matguid=30e7827a70ba4e05920d0e24fcb973c4&ckck=1

 

[chkunz]

"Also when you look up a coefficient of thermal expansion it is expressed as a change in area per degree, when in actuality the metals expansion and contraction isnt necessarily linear."

The units for coefficient of linear expansion are inches per inch per degree. Area is not a factor. Also I have not seen a reference where the coefficient of linear expansion is non linear, there may be a case where it is non linear, I just have never seen it. Do you have a reference for a case where it is non linear?

 

[Canadian bushman]

I typed that incorrectly.
Forgive me i got a lot on my plate today.

It grows in area, and is expressed as a linear equation. When the growth of the metal may not be linear over the spectrum it is described.

Area becomes a factor when applying the idea to barrels because the metal will expand or contract in all directions, and often barrels are not the same area (diameter) across its length. However the bore (ideally) is.

You can look at the presented links and see that the ratio changes with the range of temp in which the sample peice was measured. If it were linear it wouldnt change.

This leads me to believe the metal grows at a faster rate over a given range as the metal reaches its melting temperature.

When welding some metals will visibly grow or swell as they approach the melting point and i cant help but believe this same property applies over a much larger range.

I cant prove thats what happens nor do i have samples to quantify it, but i believe it as i have seen similar instances when measuring powder temp/speed.

I will often see very little or no change over a very small range of temps and then as i get closer to 40 degrees i see a huge drop in fps. Over the entire range it may factor to .7/fps, but over a 10-20 degree swing it looks closer to .2/fps.

 

[Canadian bushman]

Maybe i reaching for data on an idea that isnt there, maybe im stressing the idea of CTE to an application it doesnt apply.

Im not a metallurgist or an engineer, just a machinist with too much run time.

 

[chkunz]

Maybe i reaching for data on an idea that isnt there, maybe im stressing the idea of CTE to an application it doesnt apply.

Im not a metallurgist or an engineer, just a machinist with too much run time.

All is well. l We are all trying to learn here, my input is from a mechanical engineering text book perspective and you have machinist experience perspective. The challenge is to learn what is helpful toward accuracy. Take care.

 

['Freak]

There are a few small caveats to this.

When a tube cools, the od gets smaller and the id gets larger. The metal reduces area when it contracts. Your bullets are experiencing a similar change.

Also when you look up a coefficient of thermal expansion it is expressed as a change in area per degree, when in actuality the metals expansion and contraction isnt necessarily linear.

Just because when the metal was measured at 20* and 200* and the difference in size was recorded at "X" doesnt mean there wasnt a 40-50* span where it changed significantly less. This is typically why the CTE is presented across different ranges, and always varies.

Just food for thought.

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=M434AE

http://www.matweb.com/search/datasheet.aspx?matguid=30e7827a70ba4e05920d0e24fcb973c4&ckck=1

Thinkin’ a rifle barrel reacts dimensionally to heat same as would the barrel blank before it was ever drilled so there is/would be no inside diameter, only a center point where over a temperature change the amount of expansion or contraction at its exact center can’t help but always be zero. The coefficient of thermal expansion remains the same and applies beginning from the exact center and on out to the major diameter.

I’ll check out the links and maybe figger how I’m wrong, again, but, I still don’t think the inside diameter of a steel tube/pipe/rifle barrel ever increases as the steel’s temperature cools, it ain’t happening.

High School dropout & 'Freak

 

[Canadian bushman]

You cant assume the material will move the same after features are added. That doesnt apply a large portion of the time.

I think it depends a lot on the size of the bar and the hole passing through it.

A 2" bar with an 1/8 hole will not behave like a .5" bar with a 1/4" hole.

I cant say with certainty how each barrel of varying contours and materials are affected, but i can assure you it does happen.

 

[chkunz]

You cant assume the material will move the same after features are added. That doesnt apply a large portion of the time.

I think it depends a lot on the size of the bar and the hole passing through it.

A 2" bar with an 1/8 hole will not behave like a .5" bar with a 1/4" hole.

I cant say with certainty how each barrel of varying contours and materials are affected, but i can assure you it does happen.

I think very complicated mechanisms will deviate some from the very simple engineering examples. But a 2" bar with a 1/8 inch hole and a 1/2 inch bar with a 1/4 hole are not complicated mechanical mechanisms and the basic mechanical engineering parameters like the thermal coefficient of expansion can be depended on for analysis and for sure a first order approximation. If the simple analysis of a simple system (like a gun barrel) indicates a problem then more rigorous analysis may be needed.

 

[Canadian bushman]

Lol a lot of engineers share that same way of thinking.

Go speak with some one who cast parts and you will be baffled at how heat moves somes shapes. Often completely contradictory to what is initially believed.

Fine tolerances are always a pain regardless of how simple the features appear at first glance.

.0001 over a tube thats 100x its dia. is a ridiculous tolerance where all sorts of stuff can happen.

Thats why everyones process is so hush hush.

To know for sure, gauge a barrel, heat it and gauge it again.

Its that simple.

 

[dkhunt14]

I see posts about how temperature sensitive a powder is but often wander how much effect the barrel being subjected to the same Temps effects velocity. I realize the expansion of steel is very minimal but I would think there is some change. A tighter bore at least In my head would cause both higher pressures and more resistance. Are there any articles worth reading that take other factors into account when considering temperature.?

I saw where you cooled down or heated up ammo and the velocity changed. The barrel was cool when starting strings so the barrel did not have much effect on this.
If barrel or bore changed that much with heat, I would think you couldn't hardly hit anything with accuracy at long range on a string of fire. Like at 1000 yard BR. 7 to 10 sighters and shooting 10 records. The barrel will heat up during this. Matt

 

['Freak]

I bake aluminum 10/22™ receivers to expand the bore so an oversize barrel tenon will fall into place, then as the receiver cools and contracts about the barrel tenon, I end up with a no slop “can’t droop” resistance fit.

Same ol’ with the heating of a steel bearing race so it’ll slip onto a shaft, then it’ll cool and lock into place

And, etc., etc, ... ... ...

 

[Canadian bushman]

I bake aluminum 10/22™ receivers to expand the bore so an oversize barrel tenon will fall into place, then as the receiver cools and contracts about the barrel tenon, I end up with a no slop “can’t droop” resistance fit.

Same ol’ with the heating of a steel bearing race so it’ll slip onto a shaft, then it’ll cool and lock into place

And, etc., etc, ... ... ...

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html

Ill have to conceed to being wrong here.

The instances i have witnessed id's shrink with heat and expand with cooling must be rare anomalies.

We often heat tubing to insert carbide inserts too, id's expanding with heat is quite typical, but usually the wall thickness is quite thin compared to a barrel. I thought there could be an exception to differing thickness's of tubing, it seems i was wrong.