Understanding "barrel heat"

J

JEC

CGN frequent flyer
Rating - 100%
27   0   0
Location
Alberta
I have a bit of difficulty understanding the concept that "heavy barrels" heat up more slowly and cool down more quickly ... than "light barrels." It makes sense that a heavy barrel would be "cooler to the touch" than a light barrel because the heat has a greater mass to conduct through... but where it is important...inside the barrel where the bullet travels creating all that friction....the heat generated must be the same regardless of barrel diameter?
Are "heavy barrel" shooters who shoot longer strings just kidding themselves?
 
Well I think it would take longer to heat, but because it can hold more heat take longer to cool.
Steel is a good enough conducter of heat that the difference from the inside to the outside wouldnt be much for very long.

Heat up a quarter with a lighter and tell me if the side that you burned is hotter then the other side.

Mind you the barrel is kinda like a furnace. But from my welding days I still want to say that the outside wouldnt be too far off the inside.
 
Any barrel, reaching an elevated temperature, will start to warp. That affects the barrels POI and harmonics which in turn affects accuracy. At that point, we consider the barrel "too hot". Every barrel reacts to heat differently.

A heavy barrel has more mass then a light contour so can absorb more heat before reaching that critical temp. It will take LONGER to cool down as well since there is more mass to release heat and metal conducts heat at a farily constant rate.

So heavy barrels are used in any application where a shooter wants to be able to shoot many shots before the barrel overheats. Heavy barrels also increase the overal weight of the rifle which helps with recoil reduction too.

If all someone wants to do is take one to three shots, any barrel contour can provide the same POI/accuracy.

Jerry
 
More material in the barrel = more heat capacity. Does it take longer to boil 1 litre of water, or one cup? Same principal
 
Every barrel "whips" - to varying degrees. As the temperature of the steel changes, the harmonic of that whip will change, and thus, your point of impact will also.

A heavier barrel takes longer to change in temperature, and thus, the change in harmonic will take longer, and accuracy will be consistent for a longer time period (more rounds fired down the tube) than for a lighter mass barrel.

I think.

Although my understanding of physics and thermodynamics have been questioned in the past... Or was that me questioning Einstein? Or was it just the beer talkin'...?

;)

Neal
 
JEC said:
I have a bit of difficulty understanding the concept that "heavy barrels" heat up more slowly and cool down more quickly ... than "light barrels."
Click to expand...

To the extent that this is true the cause might be related to surface area. Internally, both light and heavy barrels have the same diameter/surface area, and the same amount of heat would be generated in either case. Externally, the heavy barrel has significantly more surface area from which heat can disburse. Steel conducts like the dickens so I doubt there's much differential throughout the barrel metal itself.
 
HKMark23 said:
To the extent that this is true the cause might be related to surface area. Internally, both light and heavy barrels have the same diameter/surface area, and the same amount of heat would be generated in either case. Externally, the heavy barrel has significantly more surface area from which heat can disburse. Steel conducts like the dickens so I doubt there's much differential throughout the barrel metal itself.
Click to expand...

Steel is actually a rather poor thermal conducter (for a metal). Still, unless you're really rapid-firing your gun, it probably has enought time to equalize temperatures, poor conductivity notwithstanding.
 
Well - the amount of steel is a function of radius squared, and the outer surface area varies with radius - so a larger barrel will take longer to cool, given comparable temps.
The controlling resistance to heat tranfer is the free convection film coefficient at the surface - doubt there is much axial temperature gradient.
 
lets not forget that a heavy barrel that is fluted has a greater surface area than a HB. that is not fluted, thus it will cool a lot faster.
 
mysticplayer said:
Any barrel, reaching an elevated temperature, will start to warp. That affects the barrels POI and harmonics which in turn affects accuracy. At that point, we consider the barrel "too hot". Every barrel reacts to heat differently.
Jerry
Click to expand...


Jerry can you let us know what you mean by "warp?"

"Every barrel reacts to heat differently" you got me on that one too. How does this relate to two barrels produced from the same lot of steel, same heat treat and same physical shape?
 
When any metal has a temp gradient across its diameter, it will "move" towards the cooler side. Hot metal expands.

Most barrels are insulated by the stock and this causes different rates of cooling. That can set up a temp gradient and thus cause the barrel to warp.

Also, barrels may not have the bore perfectly centered in the barrel. Or have the hole true with the exterior. That makes for some real fun when it heats up.

Big reason why my forends are cut away. The barrel can cool evenly over its entire circumferance.

As to the difference in barrels, you forget that there will always be difference in the machining of any barrel both internally and externally. That can set up stresses which show up as the barrel temp increases.

Something as "simple" as the deep hole boring is rarely perfectly identical between blanks. Just ask any barrel maker. Same goes for the rifling portion of the barrel making.

We assume that the grain structure of the steel is identical throughout its length and between blanks cut from the same length. For the most part that is true but what if a blank is cooled a bit faster or slower then the next chunk? What if one blank is dropped harder while cooling?

Foundries are not gentile locations where your steel is pampered.

How do you know that during the heat treating process, each barrel undergoes the same heating cycle? All kilns have a temp gradient within the chamber and the steel is stacked in different parts of that kiln. The assumption is that the temp is raised then held so that all blanks equalize but does some heat up faster?? And on it goes...

It is nice to assume that each barrel blank is the same as the last and the next but since there only a few 'hummers' from the same barrel maker, I guess there are differences.

If there weren't, Mr. Boyer would only need one barrel at a time.

Jerry
 
And I thought I was bad for miniscule issues:eek: :eek: :eek: I'm glad you provided some more detail. Definitely a finite element analysis nightmare.... lets see .001 here, .001 there .....did one cancel the other...who really knows.....wait what about the gravity as the barrel really gets hot....with the lack of a uniform taper…..then heck what about the changing dynamics as we expose the steel to these temperature gradients. Distortion might better phrase this. Don't forget porosity and irregular chemical composition.......:confused: :confused:

heck what about an eccentric case cavity (or offset/misaligned chamber) and the tendency to apply hot expanding gases off the bore center...this might heat one side of the barrel more then the other. My goodness old low quality brass like Rem.. Win. might make this a real varying problem. Perhaps the deposits of "dirty" powder, which may accumulate on the bottom of the bore......this, may insulate the barrel or retain heat.....my goodness....

With all this warping and distortion….what about the poor relatively inelastic bullet….spinning frantically in the barrel. Then, then the poorly lapped barrel….worth 0.0001 to 0.005” of varying bore diameter….heavens what are we doing….:eek: :(

With quality BR barrels, particularly heavier profiles these imperfections have less affect if any detectable. :D

As for exposed barrels, no doubt uniforming the convection coefficient has a plus but again, in most instances I doubt it is a dominating issue, again particularly with heavier barrel profiles. It’s really a toss up. In your case you are willing to sacrifice stock stiffness, create a signature look all for uniform cooling.

Cropping the forend (height or depth) of a stock from a structural prospective should be done as a gradual taper to be most efficient in retaining a balance in weight and structural rigidity.
 
Jerry, I didn't mean for you to take offence. Sorry If I offended you. I thought we were having some good discussion on the topic with a little bit of fun.
 
I have seen no real evidence of a barrel warping with continued shooting, that is, as it heats up. I have, however, seen a barrel warp significantly as a result of the insulating effect of a closely bedded forend. With this rifle, a group would be round with no tendency to walk as long as I kept shooting. If I stopped and let it cool down just a little bit (about the time it took me to walk up to the 100 yd target and back) the first shot would strike about 6 inches high, the next shot a couple inches below that, the third a couple more, and the fourth would be back to the original point of impact. Subsequent shots would stay at this group center. If I allowed the rifle to cool completely (an hour or so), the first shot would hit the intended point of impact. Once the barrel was free floated to a reasonable extent, this trait disappeared.
Given the typical clearances on most target forends (usually at least 1/16") this doesn't appear to be a factor and cooling vents or cut-away forends may have a value which is more psychological than actual. Regards, Bill
 
Bill, out of curiosity was that barrel a match barrel of a factory barrel?

I've always like the look of the cooling vents on a varmint or bench type rifle. Not so nice on finely finished sporting arm.

Are you going to be going to th Calgary show?
 
You must log in or register to reply here.
Back
Top Bottom