Heat vs thickness of barrel

[jxb]

Inside of the bore of the barrel will always heat up faster than the outside of the barrel. If I recall correctly the heat temp at the throat area every time you shoot around the flame temp is around 2200-4000F depending on the powder/cartridge etc...your not stopping what's happening inside the bore every time you light that round off.

On a temperature test we just ran exactly a year ago... it was a short test but from a cold barrel (308win was the caliber on both of them and we shot an all steel barrel and a CFW barrel at the same time and same cadence) the inside of the barrels (we measured the chamber end and muzzle end on both inside and outside of the barrels) for every 3 rounds fired the temp jumped basically 10 degrees for every 3 rounds fired. This basically applied to each one. The all steel barrel (M40/M24 contour) didn't heat up as fast as the CFW barrel by only a few degrees but once up to basically the same temp... the CFW barrel on a measured 7 min cool down period did cool to a cooler temperature than the heavy all steel barrel did.

Again though... you are not stopping what's happening to the inside of the bore of the barrel during shooting.

Later, Frank

Great info Frank, thanks for sharing. That last part is interesting. Did you test groups while doing this test to see how they differed throughout? Would be interesting to see.

 

[SteveOak]

Start with a cube, 1” on each side. The surface area is 6” square.

Make two cuts, ¼” deep and the length of the cube, both on the same face.

The area you can see when looking directly at that face is 1” still square. However, the depth of the cut has exposed four lengths of material, each 1” X ¼”. The cube now has 6 3/4 square inches of surface. (1 square inch minus what you lose at the ends.)

Similarly, when you flute a barrel the surface area of the barrel is increased.

Increased surface area will increase the radiation, if only a small amount. That is the function of fins on a heat sink, to increase surface area.

A body that radiates heat faster will retain fewer joules of energy for a given amount of time. The cumulative heating of the whole barrel, measured as temperature, will be less.

Because the thermal transmisivity of steel is low, with repetitive shots, heat will accumulate in the area of the chamber, throat and bore.

I agree that the point I am making is minor compared to what's happening to the throat of the barrel during shooting.

 

[NZ_Fclass]

Fluting will increase surface area. TRUE
The barrel should heat up slower. FALSE
will cool down faster. TRUE
and will be stiffer. FALSE

I once heard the comment from a top class F-Open shooter - "no-one ever won a match with a fluted barrel" Certainly amongst my crowd, no-one would pay to have one fluted - for little or no return, other than bling!

 

[JLT]

You are conflating the amount of heat induced into the barrel with the actual question which is the resulting temperature of the barrel.

You should probably study up on how increasing the surface area affects stiffness. An I beam will be stiffer than a rod of the same length, material and mass.

Also, I did not see structural integrity mentioned previously.

Not conflating here. If I may rephrase the question at hand for the sake of simplicity, are big fat barrels better able to deal with heat than skinny ones? The answer is unequivocal - Yes.

Let's take two 22" barrels, both chambered in .300 WSM. One is a straight 1.45", the other is a featherweight sporter contour. The former can double as exercise equipment, the latter can be swung around easily by a second grader. Side by side, on the same day, shooting the same load, one round every ten seconds for two minutes. Which barrel will retain more heat (get hotter)? We all know that answer.

Then the question of erosion comes up. Heat (retained) has some bearing in erosion of the steel in the bore, however, there is a part of the erosion that is a consequence of the violence of the reaction that produces the heat (firing the round). Much of that magic happens immediately in front of the chamber. As retained heat increases the rate of erosion also increases, for the same reason that very hot steel can be formed and shaped by a blacksmith's hammer. Two properties at work here.

Take another 1.450" blank and chamber it in .221 Fireball. If this barrel were to be mounted on a bolt action, one would have to work HARD to get that barrel anything past warm. Screw it onto something that's belt-fed, and I promise you the throat can be wrecked in short order, even though the barrel's exterior may never get very hot.

Yes, I-beams are very stiff, but there is very good reason they are oriented in a specific way in order to deal with stress. They don't do nearly as well when you lay them on their side. And you can't get an I-beam to shoot for crap . . .

 

[FrankG]

Great info Frank, thanks for sharing. That last part is interesting. Did you test groups while doing this test to see how they differed throughout? Would be interesting to see.

Yes we shot groups. Keep in mind that we just shot from the bench and the guns where not rail guns or anything like that and that we shot box ammo. For the barrel that was all steel... that was on my Accuracy International rifle. The CFW barrel was on a shop test rifle that we use. So we know the guns and how they shoot.

There where no accuracy issues from a cold barrel to a hot barrel. Guns where on call the whole time.

No handloads where shot thru them. I/we we're not trying for 1/4moa groups or anything like that. That wasn't a goal. Just good box ammo run thru good guns doing a heat test.

 

[JMA]

Yes we shot groups. Keep in mind that we just shot from the bench and the guns where not rail guns or anything like that and that we shot box ammo. For the barrel that was all steel... that was on my Accuracy International rifle. The CFW barrel was on a shop test rifle that we use. So we know the guns and how they shoot.

There where no accuracy issues from a cold barrel to a hot barrel. Guns where on call the whole time.

No handloads where shot thru them. I/we we're not trying for 1/4moa groups or anything like that. That wasn't a goal. Just good box ammo run thru good guns doing a heat test.

Frank you might be the man to answer a question I haven't gotten an answer to in the past.
Due to the fact that cm steel has significantly higher thermal conductivity than 416 ss.
Would a cm barrel be a better choice in situations where a volume of rounds are fired in a sort period of time.
M y thinking is the cm barrel would transfer the heat away from the bore much faster the the ss barrel.

thermal conductivity of 4130 = 296 BTU-in/hr-ft2-F
416 = 173 BTU-in/hr-ft²-°F

 

[FrankG]

Frank you might be the man to answer a question I haven't gotten an answer to in the past.
Due to the fact that cm steel has significantly higher thermal conductivity than 416 ss.
Would a cm barrel be a better choice in situations where a volume of rounds are fired in a sort period of time.
M y thinking is the cm barrel would transfer the heat away from the bore much faster the the ss barrel.

thermal conductivity of 4130 = 296 BTU-in/hr-ft2-F
416 = 173 BTU-in/hr-ft²-°F

Tough question to answer. I've never seen an actual scientific study per se ever done.

One thing that is a variable is the diameter of the material and how it gets effected or can be effected during heat treatment. If I recall as I'm going totally off of memory the SS heat treats easier/more uniformly vs c.m. material but on the c.m. material it had more of a variance if the material diameter was larger in size and how well it heat treated down to the core of the material/bar.

That being said...my old belief and I still kind of cling to it.... is that a c.m. barrel will last slightly longer than a s.s. barrel because they seem to take the heat better and how they wear and how they hold up to damage seems to be better. Also how the material machines... the c.m. material typically seems to be tougher to work with even when it's the same Rc spec as stainless steel is.

The c.m. vs the s.s. will wear differently or should I say show it differently. That I have seen first hand but it doesn't seem to really effect anything.... read the 2nd sentence down below....

There is no and I repeat NO!!!! Accuracy difference between C.M. or S.S. material.

Based on ammunition test barrels that we've made in identical calibers... for say 7mm Rem. Mag, 300WM, or 243win etc...the ammo/bullet makers haven't really seen a difference in terms of barrel life. Most of the pressure test barrels we make the material starts out 2.125" to 2.250" diameter. Regardless if it's s.s. or c.m. material.

In years past.... I'd say probably 90% or more of the test barrels we made out of 4140cm material but more and more customers wanted them made out of 416R now. So hardly any CM barrels are made anymore. Even the gov't changed the prints to show/allow 4140, 4150 and 416 material for the ammunition pressure test and accuracy test barrels. The only time we make any test barrels out of c.m. is if the spec is directly called out that it has to be c.m. but like I said....it's rare now for us to even get the request.

Sorry but the best I can tell you.

 

[JMA]

Tough question to answer. I've never seen an actual scientific study per se ever done.

One thing that is a variable is the diameter of the material and how it gets effected or can be effected during heat treatment. If I recall as I'm going totally off of memory the SS heat treats easier/more uniformly vs c.m. material but on the c.m. material it had more of a variance if the material diameter was larger in size and how well it heat treated down to the core of the material/bar.

That being said...my old belief and I still kind of cling to it.... is that a c.m. barrel will last slightly longer than a s.s. barrel because they seem to take the heat better and how they wear and how they hold up to damage seems to be better. Also how the material machines... the c.m. material typically seems to be tougher to work with even when it's the same Rc spec as stainless steel is.

The c.m. vs the s.s. will wear differently or should I say show it differently. That I have seen first hand but it doesn't seem to really effect anything.... read the 2nd sentence down below....

There is no and I repeat NO!!!! Accuracy difference between C.M. or S.S. material.

Based on ammunition test barrels that we've made in identical calibers... for say 7mm Rem. Mag, 300WM, or 243win etc...the ammo/bullet makers haven't really seen a difference in terms of barrel life. Most of the pressure test barrels we make the material starts out 2.125" to 2.250" diameter. Regardless if it's s.s. or c.m. material.

In years past.... I'd say probably 90% or more of the test barrels we made out of 4140cm material but more and more customers wanted them made out of 416R now. So hardly any CM barrels are made anymore. Even the gov't changed the prints to show/allow 4140, 4150 and 416 material for the ammunition pressure test and accuracy test barrels. The only time we make any test barrels out of c.m. is if the spec is directly called out that it has to be c.m. but like I said....it's rare now for us to even get the request.

Sorry but the best I can tell you.

Frank
Thanks for the answer.

 

[Webster]

Frank
Thanks for the answer.

Just shoot what the top short range shooters use and forget about the thermodynamics.

 

[JSH]

I drank the cool aid on flutes years ago as a young fellow reading every gun rag I could get my hands on. This was at a time when Dick Tracy had a wrist phone/watch, that was pure fantasy, and we knew it, if it was in a published book or magazine, it was gospel.
Forward more years than I like to admit, wrist phones are a thing and a lot of folks other than a secret agent man has them. I have also seen, witnessed or done myself, disproved many thoughts of times gone past.
A good friend of mine, retired now, was a physics professor for many years. I no longer wonder about numerous things he has explained to me so I can understand it.

There is no real replacement for “mass”.
There is no magic to getting high velocity, it is pressure plain and simple.

Fluting reduces weight, for the most part it is cosmetic and a selling point. As mentioned above you don’t see them winning matches or everyone would be doing it. How did Remingtons barrel work out some years back, build it and they will come………..for a while and then they won’t.

 

[SteveOak]

The amount of energy (heat) is independent in this case, determined by an outside agent (the chemical reaction of firing a round in the chamber). The resultant energy is a constant. What will vary is how the mass will dissipate that energy. Said differently, a round will not be 'cooler' in a fluted barrel. The greater surface area of a fluted barrel will dissipate heat (energy) more quickly, and this may appear to the observer that it 'heats up' at a different rate.

ETA - And no, a fluted barrel is not stiffer. It is not possible to increase structural integrity by removing material.

I work at an aerospace company and have the luxury of having a mechanical engineering SME (Two actually) I can talk to. He explained that I was mistaken, fluting would not increase the absolute stiffness of a barrel. It would change, and most likely increase, the resonant frequency of the barrel, which I misunderstood for stiffening.

He did confirm fluting would decrease the rate of heating of the barrel and increase the rate of cooling, due to the increased surface area. Note, from the outset I have stated clearly "barrel" and not chamber.

 

[Wild Bill IV]

My understanding is that a fluted barrel is stiffer than a barrel with the same mass and length but non fluted.

As an engineer, the structure is as strong as its weakest link!! With your argument, the fluted bbl's weak link is the distance from the base of the round nose mill cut to the bore is less than the distance of the od radius to the bore!!!! Therefore, the tensile strength is lower for the fluted bbl compared to the round bbl of same mass!!! Think of putting all you weight on a beer can!! Then, poke the can and it will smash!!! Now try to stand on a beer can with a dent, and it will crush long before you get your full weight on it!!!!
Geometrically, a round cylinder is a better shape for strength!! A perfect sphere is the best!!!! Now, for other applications, it may not be best!!! It would be too heavy for boat and aircraft bulkheads, but ideal for submarines, or it could add too much weight and increase cost in building a sky scrapper!! But the round, ribbed reinforcement rod or rebar is used to increase strength in concrete and steel applications!!!

 

[Larry Koch]

In English, fatter barrels are better.

 

[drop_point]

I work at an aerospace company and have the luxury of having a mechanical engineering SME (Two actually) I can talk to. He explained that I was mistaken, fluting would not increase the absolute stiffness of a barrel. It would change, and most likely increase, the resonant frequency of the barrel, which I misunderstood for stiffening.

He did confirm fluting would decrease the rate of heating of the barrel and increase the rate of cooling, due to the increased surface area. Note, from the outset I have stated clearly "barrel" and not chamber.

Props for coming through and admitting you were mistaken.

As far as fluting decreasing the rate of heating, I think parameters need to be stated. Would the same barrel heat more slowly after it was fluted? I'm not sure what the effect of removed mass would play.

 

[Larry Koch]

A wet towel laid over the barrel between groups in hot conditions will cool it down much faster than a air fan. And it cost nothing. When its a 110 in the shade I use Ice water from the cooler.

 

[NC/Br Shooter]

A wet towel laid over the barrel between groups in hot conditions will cool it down much faster than a air fan. And it cost nothing. When its a 110 in the shade I use Ice water from the cooler.

I missed this comment. This right here will be tried soon.
Makes sense too. Thanks

 

[gunsandgunsmithing]

Removing metal, aka fluting, does not add overall stiffness. Now, per lb, it does yield a relatively stiffer bbl but no, removing material from your existing bbl od or id will not make it stiffer. Wanna make it stiffer fast, shorten it.

 

[sandwarrior]

In this context, one can think of the barrel as nothing more than a heat sink. Two things matter (actually three, but we're limited to steel in this case) respecting the efficiency of a heat sink - mass and surface area. The greater the mass and the greater the surface area, the more efficient the heat sink. A 1.25" straight has quite a bit more mass than a 1.00" straight and materially more surface area, therefore it is a more efficient heat sink. All other things being equal, the larger tube is better able to dissipate heat than the smaller tube.

I will add that, of more concern to me are the stresses hiding in that barrel, no matter the thickness. When stresses show due to added heat point of impact changes due to different pressures on the bullet as it travels down the barrel. I know your question is pointed more towards just barrel thicknesses, but stresses internal to the barrel steel cause way more movement. That said, neither thick or thin will do better. Alleviated stresses will shoot better. when a barrel heats up.