Barrel Temperature

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bikeinxs

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Not sure if this is the right forum but I figure you guys will know the answer. What exactly is "too warm" for a barrel?

How many shots can I fire in a row? With my 270, I'll normally shoot about 3 and then wait. The barrel gets warm but not "hot". How long do you wait between shots?

How about my 222?

Appreciate any guidance.

Thanks.
 
I think it is more of an accuracy concern than barrel life concern. Barrel burning is done at temperatures well in excess of 1000 F, and in milliseconds, not minutes. An initial temperature elevation of 100F probably does not change things much. Auto or semi-auto firing is likely where the barrel burning effect starts to take a toll.

On accuracy it is much more complicated. I like to see the barrel elevate to a warm state, and then shoot at a more constant rate to keep it about the same temperature. You have to balance that against changing wind conditions. The diameter of the barrel also makes a difference. My theory is that a fat barrel actually shrinks the bore if you shoot fairly quick consecutive shots. The outside stays cold, while the inside heats up and has to go somewhere, so it shrinks the bore. This in turn raises pressure and velocity. All considered not a simple subject, when you start to think about accuracy.
 
I have personally seen a barrel get to temps where running patches of bore cleaner through it were making the cleaner sizzle as it went through during a hot day of load development.

This particular barrel won the BCRA F-Class Championships, Lt Gov's Prize and came 2nd place in the WCFC in Winnipeg this past season.
 
Ron AKA said:
My theory is that a fat barrel actually shrinks the bore if you shoot fairly quick consecutive shots. The outside stays cold, while the inside heats up and has to go somewhere, so it shrinks the bore. This in turn raises pressure and velocity. All considered not a simple subject, when you start to think about accuracy.
Click to expand...

Sorry Ron but when the barrel heats up the bore gets bigger not smaller. Not theory but fact.
 
Calibre has a huge impact on the barrel too, not just temp. I have a Weatherby Mark V in .257 WM and with only 300 rounds down the tube well spaced at 3-10 minutes apart there is significant heat cracking the first 3-4 inches of the barrel already. The barrel was never let get hot at all. Just as a note, this barrel to the naked eye looks perfect, but with the borescope all kinds of nasties are visable.
 
I shoot in competiton. The rate at which the rifle is fired is pretty much determined by the match conditions. The barrel can get pretty darn hot at times.

.257 Weatherby is a seriously overbore cartridge. Fortunately a hunting rifle seldom has to fire a rapid string of shots, and a big game rifle can be used for years without running the round count up too fast. I suspect it would be a poor choice for a prairie dog rifle.
 
"Too warm" is when it gets hot enough for rounds to cook-off when they are chambered. Not likely to happen with a bolt actioned rifle. I was wttness to the aftermath of a 50 cal HMG round cooking-off, and the unfortunate victim was blinded in one eye as a result.

Heat = dramatically increased wear. You can shoot your rifle hot, but understand in doing so you are dramatically reducing its accurate life span.

Hunitng rifles are neither designed nor intended for shooting 20 shots in 60 seconds. Let them cool to the point where you can hold them indefinitely. If a barrel is too hot to hold, then I tend not to shoot it until it has cooled.

Many factory barrels (Ironically, hevay barrels seem to be worse) have latent stresses in them that actually cause the POI to change, due to dimensonal changes withn the barrel. This is why competitive precision shooters use stress-relieved heavy contoured barrels.
 
maynard said:
Sorry Ron but when the barrel heats up the bore gets bigger not smaller. Not theory but fact.
Click to expand...

What you say is true once the whole barrel cross section gets hot. The bore expands larger the exact same amount as if the bore was solid steel.

However, what I was referring to was the transient condition where the metal near the bore is hotter than the metal surrounding it. The strong colder barrel near the OD does not expand, and the warmer metal actually expands inward, causing the bore to tighten temporarily. This happens when you shoot successive shot quickly. It affects pressure, velocity, and as a result accuracy. The effect is more significant in a thick target barrel.
 
If you can cook bacon hanging off your rifle barrel- it is too hot!
If your barrel is glowing red- it is too hot!
If it gives you second degree burns when you touch it- it is too hot!
 
You are both right

maynard said:
Sorry Ron but when the barrel heats up the bore gets bigger not smaller. Not theory but fact.
Click to expand...

When the inside of a bore is blasted with heat, the heat expanded metal has no place to go initially but in. As the heat transfers outward enough to expand the whole barrel, then the bore gets bigger. Bear in mind that we are talking about very small amounts of change. This subject was covered in a thread at the accurateshooter forum by credible people.
 
For load develpment I have started to notice changes on factory barrels when it is warm on the hand, not even close to hot. For a sporter type wsm type rifle I usually shoot 2 and then let it cool. This is an extreme senario.
 
Well - The thermal conductivity of steel is very high - you would have to work hard to get a large enough thermal gradient in the radial direction to get the bore to contract under sustained fire.
As per the OP's post - keeping the barrel at constant temp will benefit accuracy. That means you get two or three warm up shots in relatively quick succession, then you have to wait between shots. However, if you've got an expensive match rifle you can likely get way with fluctuations in barrel temp - thats what you've paid for!
 
I'd say that regardless of whether it's too hot to touch or just hot, if the point of impact shifts enough that it's unsatisfactory, then it's too hot for your gun. Some barrels seem to be able to take more heat than others before this occurs. If yours starts to wander on the 3rd shot, then perhaps that's your limit.
 
"...when it is warm on the hand..." Warm isn't too bad. Hot to the touch is.
"...barrel is glowing..." MG's have been known to cook off the ammo at those temperatures. Barrel is ruined too. Mind you, the troopies don't care and M60 barrels are easily changed.
 
Any soldier who gets a barrel glowing that hot, was either in deep trouble looking to get out, or looking to get into trouble!
 
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