Barrel thickness vs heat damage

[1shot]

Forum boss,
If I put this in the wrong category, I apologize in advance. If so, please move it to the correct area.

I may be wrong here :-\ but I think it’s probably an accepted fact that heat from fast sustained string of fire do damage to the throat and the first 3-5” of rifling of the barrel. For the sake of this post, I’m talking about L-R sling/prone shooting or F-class matches where a shooter can and sometimes fires as fast as he can get pit service for 15-20 rounds plus sometimes unlimited sighters. I say this because I am wondering what contour allows for the least amount of damage. For instance do you go with a light Palma contour to save on weight and the barrel gets hot faster, or a heavy contour that takes longer to get hot, but holds the heat longer? I’m sure a lot of this is going to be theoretical, but I’ve been scratching my head about this long enough. Any thoughts, opinions or actual hard data would really be appreciated.
Thanks,
Lloyd

 

[Plugger]

I would think a heavy barrel with fluting would help with the heat.

 

[Steve Blair]

Each cartridge imparts a specific heat input to the barrel as it is fired. Although stainless steel is considered a poor metallic heat conductor, it conducts much better than the air around it. The heat imparted to the barrel by firing will attempt to reach equilibrium within the barrel, until the entire barrel is the same temperature. All damage is done to the barrel only a few thousandths deep in the throat and first few inches of the rifling. The faster the heat can migrate away from that area, the better. As such, the greater the barrel's mass, the more heat it can contain at lower than damaging temperatures. The rate at which heat is conducted away from that area is affected by the latent heat in the rest of the barrel. If the barrel is cold, heat will be conducted away quickly. If the barrel is too hot to touch, not as quickly.[br]
Concerning heat conduction away from the barrel: the larger the diameter, the greater surface area and more heat that can be conducted to air. This is much slower than within steel but can still move significant heat away from the barrel. Flutes increase surface area but also decrease mass. If the heat input will be accomplished quickly, a solid barrel is the better choice. If the heat input is slow, flutes are probably a better choice. Unfortunately, F-Class falls in between and has weight limits. So, the correct answer is less obvious. [br]
I shot twenty shot matches when the temperature was in the mid nineties and came away from the line with a barrel too hot to touch. The same when shooting two relays with provided pullers and the barrel never cooled much between strings. I know that these events contributed to the barrel's demise, but there was little to do about it. Sadly, the barrel is a consumable item, nothing will make it last forever except not shooting it. If you know the day will be hot, take an ice-filled cooler with you (drinks optional) and a small towel. Soak the towel in water and put it in the ice chest. Between relays, drape the towel over the barrel, avoiding the muzzle. Water is a good heat conductor and will pull a lot of heat quickly from the barrel. This will not affect the barrel's temper in any way.

 

[Immike]

I have to agree with the heavy barrel for heat dispersion by way of volume. To speed up the cooling I place my rifle in a upright holder on my cart so the barrel gets the chimney draft through the bore. Mike

 

[4xforfun]

I agree, as heavy as practical. Now, as far a fluting a BBL....I have absolutely no scientific proof, but I get a LOT more BBL mirage when I shoot fluted bbls that are hot, or even warm, vs non fluted bbls. The fluted tubes really shed the heat. Use of a mirage shade is mandatory when using a fluted tube.

Just my .02

 

[SS427]

I've read on this website and a few other places that a bead blasted barrel, or one with the snake skin pattern engraved on it, will shed heat even faster than a fluted barrel. This is because the pits caused by the bead blasting increase surface area significantly. 4xforfun presents observable data that a fluted barrel sheds more heat. Anyone notice this same effect with a bead blasted barrel?

 

[Plugger]

Then I guess a large dia. barrel ,fluted, then bead blasted would dissipate the most heat, huh!

 

[4xforfun]

I have had Clay Spencer do lots of work for me and he has told me on numerous occasions that the bead blasting does indeed dissipate heat. The tubes I get from him are bead blasted with non bead blasted flutes.

 

[Turbulent Turtle]

(snip some excellent and well thought out stuff.)

The same when shooting two relays with provided pullers and the barrel never cooled much between strings. I know that these events contributed to the barrel's demise, but there was little to do about it. Sadly, the barrel is a consumable item, nothing will make it last forever except not shooting it. If you know the day will be hot, take an ice-filled cooler with you (drinks optional) and a small towel. Soak the towel in water and put it in the ice chest. Between relays, drape the towel over the barrel, avoiding the muzzle. Water is a good heat conductor and will pull a lot of heat quickly from the barrel. This will not affect the barrel's temper in any way.

We encounter such situations a lot shooting in south Texas. In my rifle case, I carry a bubble machine that I picked up at the local Wal Mart for about $8. It's in the fishing section and it's used for aerating pails of bait. I pulled out the stone and inserted the hose in an old rod guide with yello tape. It's amazing how quickly a barrel cools with this gadget.

 

[Steve Blair]

We encounter such situations a lot shooting in south Texas. In my rifle case, I carry a bubble machine that I picked up at the local Wal Mart for about $8. It's in the fishing section and it's used for aerating pails of bait. I pulled out the stone and inserted the hose in an old rod guide with yello tape. It's amazing how quickly a barrel cools with this gadget.

[br]
When I visited the Steyr factory in the late eighties, they had a fixture for cooling AUG barrels overheated during test firing. A copper tube, connected to their shop air supply, ran alongside a fixture to cradle the barrel. The tube had a series of holes facing the barrel and the end curved 180° and provided the breech support by entering the chamber. The muzzle end was supported on a "V" block. When the barrel was located on the fixture, a valve was turned and compressed air flowed over and through the barrel for ten or fifteen seconds. You could then touch the barrel without a glove, even though it had been far too hot to touch. [br]
I think this is the stationary version of your field expedient. The only thing I don't understand is how it keeps your drinks cold.

 

[Turbulent Turtle]

I does not keep the drinks cold, but they are well aerated.

 

[6MMsteve]

I follow the guy with the cooler, hoping for a handout

 

[Zilla]

I follow the guy with the cooler, hoping for a handout

This.

 

[dkhunt14]

Rate of fire is the biggest wear on a barrel. I believe the internal temp from the fire going across the throat is what wears them. A thinner barrel would get hotter quicker but I don't believe you would see much difference in wear of a barrel unless the diameters were far apart. I would be more concerned on heat making the barrel walk. Matt

 

[wapiti25]

shoot small cartridges less powder less heat.

 

[Ggmac]

I'd forget about fluting , today it's just ornamental . Cooling or I should say better cooling can be accomplished by fairly coarse external threading , bead blasted , black surface treatment . Think air cooled fins on. Motorcycle . It may not be pretty but it does decrease the temp vs polished SS .

 

[RDavies]

I'd forget about fluting , today it's just ornamental . Cooling or I should say better cooling can be accomplished by fairly coarse external threading , bead blasted , black surface treatment . Think air cooled fins on. Motorcycle . It may not be pretty but it does decrease the temp vs polished SS .

These will all help to decrease barrel heat as mentioned, but at what point does an increase in dissipating barrel heat start to cause more trouble with barrel heat mirage than it is worth?

 

[spclark]

...but at what point does an increase in dissipating barrel heat start to cause more trouble with barrel heat mirage than it is worth?

Interesting point but in thinking through it I surmise there's more value in getting heat load dissipated fast, reducing the time before mirage diminishes, over having heat remain in a barrel over a longer period which inevitably will prolong mirage.

Mirage bands and 'scope objective tubes are worthwhile aids to diminishing mirage effects, the former particularly as they can be run full-length by those of us who shoot match sights.

I do rather like the bubbler idea though! Adding air cooling thru a bore between strings ought quickly to help pull latent heat from barrel steel. On a really hot day it may even be of value during a string if conditions permit. (I carry a little battery-operated fan for days like that... set up opposite my spotting scope, it blows air onto my face when I'm in position, sweating out wind doping while waiting for my target to get marked then re-appear.)

 

[Ggmac]

Problem arises when you cool too quickly . Thermal expansion and contraction is the fire cracking you see in the throat . The high heat generated by the firing is of course higher on the surface ( bore ) and gradually radiated to the exterior . Rapid cooling exaggerates this fire cracking .
I don't have the answer , but have expermented , 2 barrels , same boe cartridge , make , diam ,length .
Fire 20 round strings , one barrel was cooled rapidly with cool water , actually dipped the entire barrel in chilled water , the other left to cool naturally . Both were then allowed to air coll to equal temps .
After 2 months and 450 rounds , I stopped . I bore scoped every 100 rds .
In the end ,I cut the 3 1/2 " off each chamber and milled 1/2 off to reveal the chamber and throat .
The results were clear , fast cooling increased the bore erosion
I know this is the extreme cooling but at some point it demonstrates the surface thermal cracking is increased with rapid expansion and contracting

 

[JarheadAZ]

Here's an established approach....

Greg