how long before barrel heat affects accuracy

As the title says? I am curious to know when barrel heat starts to affect accuracy and when damage begins.

Reason I ask is I have the new .270 and I sighted it in with cheapy Winchesters and recently purchased what I think is a good round for Bear. Sako hammerheads 156 gr. I was sighting the gun in last Saturday in the rain (time is limited) and the I may have only fired 9 or so rounds to zero at 70 yards but wholy crap the barrel was hot. was actually steaming as the rain would hit it. Outside temperature was maybe 8 degrees. I don't believe I could have caused any damage after 9 rounds, but I am really curious to know when is too much.

You'll have to shoot a lot...lot more higher velocity rounds before you'd ever come close to permanently affecting the barrel.

Typical magnum calibers, and know "hot" loads will eventually start to have an effect. But for a relatively moderate round like the .270, you're GTG for a few 1000 more. Now if you're asking how much heat affects a barrels consistency, then yes, allowing barrel to cool in between shots is optimal.

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Originally Posted by Bluebulldog

. Now if you're asking how much heat affects a barrels consistency, then yes, allowing barrel to cool in between shots is optimal.

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Even that is subjective to what you consider 'accuracy'....at 70yds shooting sub-moa, it would take a whack of shooting before you notice the group size growing beyond MOA, at that distance.

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Originally Posted by MikePal

Even that is subjective to what you consider 'accuracy'....at 70yds shooting sub-moa, it would take a whack of shooting before you notice the group size growing beyond MOA, at that distance.

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Very true. I think the Op gets the picture though.

I wonder where this worry comes from. In the military we used to shoot belts of ammo, boxes of mags one after the other and never once was there a concern about the barrel over heating. At least not in the smaller calibers.

The only time I know there was a drill for removing an over heated barrel was with the .50 cal belt feed guns.

Barrels may be hot to the touch, but those temps are far below the temps required to affect the barrels integrity. It would have to be almost glowing red.

When I clean my ML fluted barrel I use a kettle of hot water, as I pour it down the barrel I cannot hold on the barrel bare handed. They are designed to dissipate heat quickly.

The mirage in the scope created from the hot barrel would effect your accuracy before you hurt the barrel. For the first few hundred rounds the barrel will warm up quicker till it is broken in.
The machining marks still need to be smoothed out in the lands and grooves.

3 to 4 rounds from a .270 will make the barrel hot to the touch. Typically, I will shoot 3 or 4 shots, wait ten minutes to cool, then shoot another group.

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Originally Posted by Kilo Charlie

3 to 4 rounds from a .270 will make the barrel hot to the touch. Typically, I will shoot 3 or 4 shots, wait ten minutes to cool, then shoot another group.

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Hey KC, have you ever noticed a difference if you continue to shoot with a hot barrel....I had a guy on the range one day tell me that it did, but after awhile I saw it wasn't the 'heat' as much as shooter fatigue causing his rounds to climb.

By taking a break after 5 rounds to cool down the barrel, it also allows you to stretch out a bit before the next set.

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Originally Posted by MikePal

I wonder where this worry comes from. In the military we used to shoot belts of ammo, boxes of mags one after the other and never once was there a concern about the barrel over heating. At least not in the smaller calibers.

The only time I know there was a drill for removing an over heated barrel was with the .50 cal belt feed guns.

Barrels may be hot to the touch, but those temps are far below the temps required to affect the barrels integrity. It would have to be almost glowing red.

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I always found it funny. On the Machine Gunners course, you'd carry the spare barrel for the C6 with the expectation of barrel change out after every 3 or 4 belts.

.....never actually happened unless you had the course O walk by.....

Accuracy isn't really your leading concern with a C6. :)

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Originally Posted by welsh

Accuracy isn't really your leading concern with a C6. :)

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Exactly, it's spray and pray that you had put out enough lead in the area to keep the enemy's heads down.

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Originally Posted by jaycee

Exactly, it's spray and pray that you had put out enough lead in the area to keep the enemy's heads down.

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With the turret mounted .50, we would engage 'full auto' at a 13'x8' dumpster at 500 yds with belt feed ammo having a tracer ever 5 rounds. In a night shot, you could see the accuracy fairly clearly and was quit impressive.

However, after a few hundred rounds you got to see what happens when the barrel got 'red' hot and the bullets would start to tumble.

If interested, take the case capacity in grains of water divided by the area (in sq. in.) of the bore cross-section. This gives you an number which lets you compare various cartridge types. Any Number under "900" is mild as far as "barrel burners" and anything over "1000" is hard on barrels.

It more about the pressure, temperature and powder burn at the chamber throat /leade than the barrel heat itself. (except of course what has already been mentioned about shots walking off zero after about 3-5 rounds, especially with light sporter contoured barrels.) It is also about how much precision you are looking for and measuring against in order to determine "harm"(non repeatable accuracy)

Big capacity cases and little bullet calibers eat/erode) barrels quicker and even much faster than that, if continuously shot hot.

For example one may get 20,000 rounds out of an AR 15 if shot reasonably before it keyholes, although I have seen high dollar, name brand ones go at 10,000 rounds. On the other hand numerous name brands seldom last past 1000 rounds on continuous full auto.

It is all about the heat and pressure eating away at the metallurgy.

I shoot a med. contoured .260 and I try to limit continuous shots to one magazine(10 rds) or less. The .268 SPC auto's max is about 60 before a long cooling break.

If you are sighting in for hunting and stretching your range out then you want to be sighted in the same way as you would hunt, with a cold barrel. You will be taking 1 shot on that deer, not 9 or 20. That being said, once you sight it in then take 10 shots rapidly and see on that 11th shot how far your accuracy is off, it probably will be fine, your POI will be slightly different but not that much different. As for hurting the barrel you will be fine, look at all the military rifles with military barrels that are 70+ years old and fired rapidly for all of their military service life, they still shoot fine as long as the crowns are good and they are not shot out from corrosive ammo.

Your 270 got hot because it is a sporter profile barrel, narrow and light, nothing wrong with that, heats up faster than a heavier barrel but for hunting it is the perfect design, no worries at all.

If 9 round wrecked a barrel there would be a lot of guys in the Eastern Ontario deer woods with clubs rather than rifles, deer on the run make for a bit of excitement if you are trying to sneak a nap :)

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Originally Posted by Kilo Charlie

3 to 4 rounds from a .270 will make the barrel hot to the touch. Typically, I will shoot 3 or 4 shots, wait ten minutes to cool, then shoot another group.

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X2, I find with my sporter barrel 270 after 2-3 shots it starts to open up the group abit. The first shot or two from a cold barrel is all that matters when hunting. I like a bedded free-floating barrel on my bolt guns

How many rounds that you can fire before groups open up or damage to the barrel occurs are two very different things... Generally speaking going on long strings of fire with "sporter" contour barrels generally will result in enlarged groups but the amount of shots required and the rate of fire of the strings are really up to you to figure out since every barrel/gun will behave differently.

For damage to occur, you really need to heat that sucker up, like too hot to touch hot and keep going... Generally the throat of the chamber starts to erode, the rifling near the chamber and at the end of the muzzle then start to go. This is what happens over time when shooting due to wear mechanisms caused by the heat and chemically affected zones in your barrel; by running smoking hot and abusing the out of your gun, you accelerate the rate at which this occurs.

For example, a .223 can generally go up to 10k rounds before any "noticeable" accuracy degradation occurs(using a stainless barrel for example), of course that depends on the barrel material and cleaning regime. That same barrel though, could get "used up" in as little as 2k rounds or less if you really wanted.