Proof Carbon vs Steel barrels

[Wind Gypsy]

That’s an interesting question: does the CF insulate the barrel, holding the heat IN?

Maybe some? I know mirage seems to become an issue faster with carbon barrels which would indicate they shed heat faster. My gut feel based at reading about this is the bore on a carbon is going to heat up faster than a comparable weight steel barrel because it has less steel to disperse the heat. I also expect them to cool faster for the same reason and the carbon doesn't seem to be enough of an insulator to prevent that from happening.

This phenomenon is obvious with steel barrels comparing a sporter to a heavy contour. Heavy barrel heats up a lot slower but if you get it piping hot its going to take a lot longer to cool down too.

 

[brockel]

You can get to your goal of 7.5# with a steel barrel. I have a 17” 6.5prc that’s just shy of 8lbs with a leupold vx5hd and a banish 30 on it. Lighter weight scope would get it there. If you have to have the carbon fiber barrel there are better choices than proof

 

[Elkmagnet]

Maybe some? I know mirage seems to become an issue faster with carbon barrels which would indicate they shed heat faster. My gut feel based at reading about this is the bore on a carbon is going to heat up faster than a comparable weight steel barrel because it has less steel to disperse the heat. I also expect them to cool faster for the same reason and the carbon doesn't seem to be enough of an insulator to prevent that from happening.

I don't know that there is really an answer it looks like carbon fiber can be made to conduct heat better than steel but can also be used as an insulator depending on its makeup.

Understanding Carbon Fiber Thermal Properties

Understanding the thermal properties behind carbon fiber composites can help engineers make the right design decisions for their end applications.

www.tencom.com

"For instance, high thermal conductivity carbon fiber is often used in electronics to dissipate heat away from sensitive components. On the other hand, low thermal conductivity carbon fiber is ideal for insulating applications where heat needs to be contained"

 

[pyrotechnic]

Carbon is not an isotropic material like steel, so the orientation of the fibers and the makeup of the epoxy have a huge effect in both it's mechanical and thermal properties.

 

[Wind Gypsy]

You can get to your goal of 7.5# with a steel barrel. I have a 17” 6.5prc that’s just shy of 8lbs with a leupold vx5hd and a banish 30 on it. Lighter weight scope would get it there. If you have to have the carbon fiber barrel there are better choices than proof

I know TS Customs was happy with benchmark carbons thus far while back which are also light like proofs. I'd personally go bartlein but the lightest bartlein isn't particularly light.

 

[WapitiBob]

Get a #4 Bartlein carbon if you want light. A 26" carbon Sendero is the same weight as a 26" #3 steel.

 

[yakimanoob]

I know mirage seems to become an issue faster with carbon barrels which would indicate they shed heat faster.

Quite the opposite. The intensity of mirage is directly related to the temperature difference between the air and the barrel, other things being equal (it's worth noting that the color of the material is usually not equal and has a big effect on thermal radiation, but that's beside the point).

More mirage means the difference in temperature is greater, which, assuming the same number of shots in the same time frame, same atmospherics, etc., means the barrel that produces more mirage sheds heat slower.

 

[yakimanoob]

Carbon is not an isotropic material like steel, so the orientation of the fibers and the makeup of the epoxy have a huge effect in both it's mechanical and thermal properties.

While it's true that the thermal conductivity of CF is variable, it does not mean that carbon fiber barrels can be made to shed heat as fast as steel. (it's also worth noting that "steel" is not isotropic either - alloying formulations affect thermal conductivity).

Insulation or conduction is a relative thing. All materials conduct heat; we just call them thermal conductors if they conduct heat faster than other things, and we call them thermal insulators if they conduct heat slower than other things. Aluminum is used for heat sinks because it conducts relative to most other materials. Styrofoam insulates relative to most things, which is why we use it for coffee cups and a bajillion other things.

CF insulates relative to steel (usually by a factor of 10 or so, although certain formulations can be much closer).

 

[pyrotechnic]

Quite the opposite. The intensity of mirage is directly related to the temperature difference between the air and the barrel, other things being equal (it's worth noting that the color of the material is usually not equal and has a big effect on thermal radiation, but that's beside the point).

More mirage means the difference in temperature is greater, which, assuming the same number of shots in the same time frame, same atmospherics, etc., means the barrel that produces more mirage sheds heat slower.

This doesn't pass my sniff test. It's been a while since I took heat transfer and I don't use it professionally on a daily basis, but if convection is occurring at a higher rate at the barrel surface (because the surface is hotter), and there was equal heat input at the "center" of the barrel, then conduction through the barrel would need to be occurring at a higher rate as well.
An insulator would keep the disparity in temperature between the center and the surface higher for longer, and reduce heat loss at the surface. This is why we use an oven mit to grab a hot pan out of the oven and insulate our houses to keep them warm.

 

[pyrotechnic]

While it's true that the thermal conductivity of CF is variable, it does not mean that carbon fiber barrels can be made to shed heat as fast as steel. (it's also worth noting that "steel" is not isotropic either - alloying formulations affect thermal conductivity).

Insulation or conduction is a relative thing. All materials conduct heat; we just call them thermal conductors if they conduct heat faster than other things, and we call them thermal insulators if they conduct heat slower than other things. Aluminum is used for heat sinks because it conducts relative to most other materials. Styrofoam insulates relative to most things, which is why we use it for coffee cups and a bajillion other things.

CF insulates relative to steel (usually by a factor of 10 or so, although certain formulations can be much closer).

I am not sure if CF barrels can be made to shed heat faster, I haven't measured it using any method beyond "that carbon section feels hotter than the steel shank next to it". I don't manufacture carbon fiber products, and I don't know a whole lot about it as a material other than fiber orientation matters and certain versions of carbon are incredibly conductive to heat while others are not, but that can be dependent on the orientation within the carbon material itself, and then again dependent of how the carbon fibers are oriented within the composition material with its matrix.

As far as your steel comment goes I'm not sure you understand what isotropic means. Different alloys of steel do have different properties. In a bulk sample, they display those same properties in all directions. That is an isotropic material

There may be exceptions as to when those properties do not hold in all directions, but for the purpose of heat conductivity in a rifle barrel, i doubt that we would find those exceptions of any use.

 

[badkarma6]

So I built a reasonably priced rifle with a short barrel in order to take a suppressor. I did not go with a carbon fiber barrel as the barreled action I bought came with a heavy steel barrel that does well with a suppressor.

1. I bought a Howa 1500 barreled action in 6.5mm Creedmoor with 16.25" barrel - $450 - https://www.brownells.com/gun-parts...ts/m1500-6.5-creedmoor-16.25-barreled-action/
2. MDT Field Stock - $300 - https://mdttac.com/mdt-field-stock-chassis-system/
3. The Howa trigger that the barreled action came with wasn't bad but I decided to upgrade to a Timney Trigger - $175 - https://timneytriggers.com/howa-trigger-upgrade/
4. Talley Picatinny Base - $50 - https://www.amazon.com/gp/product/B00DB81N72/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1
5. $975 for all that. Both the scope and suppressor that I added cost more than the whole setup.
6. I mounted a Vortex Razor LHT 4.5-22x50mm scope on it
7. Used a CGS Hyperion Suppressor
8. Harris bipod
9. Result - it will consistently shoot a 5-shot 1" group @ 100 yds. Likes 120gr ammo the best.

 

[yakimanoob]

As far as your steel comment goes I'm not sure you understand what isotropic means. Different alloys of steel do have different properties. In a bulk sample, they display those same properties in all directions. That is an isotropic material

Ah, I see. Thanks. I jumped to the conclusion that isotropic effectively meant that carbon fiber means lots of different things depending on formulation but steel is all the same. My mistake .

 

[yakimanoob]

... if convection is occurring at a higher rate at the barrel surface (because the surface is hotter), and there was equal heat input at the "center" of the barrel, then conduction through the barrel would need to be occurring at a higher rate as well.

Not necessarily. It's true that the surface of a barrel with higher thermal conductivity will get hot faster than the surface of a barrel with lower conductivity, assuming the same energy input in the bore, but

1. this is true ONLY if you hold the other thermodynamic variables constant. It's important to remember that the heat capacities, not just the conductivities, are very different between the two materials in question.
2. if we do hold all those other variables constant, it is also true that the barrel with the higher conductivity cools down faster than the barrel with lower conductivity for all the same reasons.

Each time we send a round, we're giving the bore a little boost of thermal energy. Steel is much better at conducting heat from the bore to the atmosphere, so while it reaches its peak temperature faster, it also sheds that heat faster. A CF barrel will hold on to the heat for longer, which means each time we send an additional round, we're stacking a little more heat onto an already hot barrel.

An insulator would keep the disparity in temperature between the center and the surface higher for longer, and reduce heat loss at the surface. This is why we use an oven mit to grab a hot pan out of the oven and insulate our houses to keep them warm.

This is certainly true. But it only takes once to learn that if you have a thin oven mitt and a hot, heavy dutch oven, you have to be quick! This doesn't mean we call the oven mitt a thermal conductor.

 

[Wind Gypsy]

Each time we send a round, we're giving the bore a little boost of thermal energy. Steel is much better at conducting heat from the bore to the atmosphere, so while it reaches its peak temperature faster, it also sheds that heat faster. A CF barrel will hold on to the heat for longer, which means each time we send an additional round, we're stacking a little more heat onto an already hot barrel.

Assuming you're comparing to a steel barrel of equal weight in this instance? If so that makes sense to me. I'm pretty sure ive seen tests comparing carbon to steel of similar contour (I.E. much heavier) and the steel barrel both heated up slower and cooled down slower than the carbon.

 

[yakimanoob]

Assuming you're comparing to a steel barrel of equal weight in this instance? If so that makes sense to me. I'm pretty sure ive seen tests comparing carbon to steel of similar contour (I.E. much heavier) and the steel barrel both heated up slower and cooled down slower than the carbon.

Generally speaking, a less dense material will insulate relative to a more dense material, other things being equal. Carbon fiber has ~40x lower thermal conductivity, ~2x higher specific heat capacity (meaning it takes twice as much energy transfer to heat/cool a gram of CF by one degree than a gram of steel by the same amount), and ~4x lower density.

Taking all three of those properties together, this means that steel moves heat from the bore to the surface 40x faster than CF, and it takes about twice as much heat transfer to cool a CF barrel by the same temp delta as a steel barrel, assuming the geometry of the two barrels is identical. I'd be very interested to see a test like the one you mentioned, as all the ones I've seen show the opposite result.

 

[PRO MO]

nerds. just tell us which one is best

 

[yakimanoob]

nerds. just tell us which one is best

At least I didn't bring inferential statistics into it. If you want me to, I can .

 

[yakimanoob]

But to the point of which is better, it's worth noting that thermal properties are ultimately not what we care about. How all these thermal properties affect accuracy is the important thing at the end of the day, but that's way more complicated and will depend on the individual weapon.

 

[Wind Gypsy]

nerds. just tell us which one is best

carbon fiber barrels heat up faster and cool slower than a comparable weight steel barrel.

Alex wheeler did deflection tests to test stiffness and came away with the conclusion that the carbon barrels he tested weren't stiffer than a comparable weight steel barrel.

The process of turning a barrel down to a very thin core and then wrapping it with carbon fiber is additional opportunity to add stresses in barrel steel.

lots of people think carbon fiber looks cool.

You are less likely to need to spend an additional $50-100 to get an acceptable shoulder to index a muzzle device against with common 5/8" threads on carbon barrels than a similar weight steel barrel.

Carbons frequently cost $350 more than a comparable quality steel.

So if what you or other people think looks cool is more important than saving $250+ and having higher odds of better mechanical precision and perhaps better better barrel life, carbon is best.