how do you measure barrel temperature in a reliable manner?

[jdavistx]

I think we're talking about 1 barrel here. Sorry, no apples in the house. How about a grapefruit, an orange, and a wall? The orange was 1/10th of a degree lower. The point is, it's a reference and a pretty good one.

An IR temp sensor is inconsistent across different finishes and types of surfaces. Readings from bead-blasted and blued vs. polished and blued vs. bead-blasted SST vs. cerakote in any particular color will all be different when the metal's actual temperature is the same. Can use them to compare the same apple at different times. Can not use them to compare two different apples in any meaningful way. Forget about comparing an orange with one.

 

[ntsqd]

The point is that different metals and different surfaces have different emissivities. Some will be fairly close to the same while others are far different and you can't compare a reading from one rifle to the reading from another unless their materials and surface finishes are the same. Even then there can easily be a small difference that likely won't matter for this use, but it there all the same. If all you're doing is taking readings from one rifle then this doesn't matter. As soon as you want to take a reading from a second rifle and compare it to the first then now it matters. How much it matters depends on the different emissivities.

Where I learned this was in comparing a machined aluminum part to a cast aluminum part that were bolted together. There was a difference in those readings that was significant to what we were doing (~10°) and it had us chasing our tails for a while. Simply Scotch-Briting both surfaces and then putting a spot of flat black paint on each got the two readings to agree.

 

[jdavistx]

The point is that different metals and different surfaces have different emissivities. Some will be fairly close to the same while others are far different and you can't compare a reading from one rifle to the reading from another unless their materials and surface finishes are the same. Even then there can easily be a small difference that likely won't matter for this use, but it there all the same. If all you're doing is taking readings from one rifle then this doesn't matter. As soon as you want to take a reading from a second rifle and compare it to the first then now it matters. How much it matters depends on the different emissivities.

Where I learned this was in comparing a machined aluminum part to a cast aluminum part that were bolted together. There was a difference in those readings that was significant to what we were doing (~10°) and it had us chasing our tails for a while. Simply Scotch-Briting both surfaces and then putting a spot of flat black paint on each got the two readings to agree.

That would definitely have you chasing your tail.

 

[xsn10s]

That's interesting information on the ir temp sensor. I've seen them at the different companies I worked at but I never used one. I guess if you kept records of each barrel and consistently used the same spot it would give you some valuable data. I generally use the hand temp sensor. But I keep the trigger fingers off the barrel. Though I don't do this it could show some valuable information.

 

[Hugnot]

I would use an IR thermometer on numerous locations on my one piece barrels. Should the barrel be shiny & reflective I would test out temp differences on both bare shiny surfaces and those having a light coating of powdered lamp black. I would assume inner bore surfaces would be frying hot. I have a few light flyweight barrels that were replaced by heavier barrels because the flyweight barrels heated up quickly and then accuracy went away.

 

[ATH]

I don't.

The issue is irrelevant for hunting rifles, I simply take my time on the range so heating is never an issue as when I hunt the gun will be cold so I want important shots to be representative of that condition. With high powder capacity rounds I'll take 3-5min between shots.

I see a lot of unsubstantiated assumptions in this thread, like barrel temp affecting MV. I shoot F-class and on my first string with unlimited sighters it's typical to put 25-30 rounds of 284Win down range in 15 minutes. Granted it's a 1.25" cylinder barrel but I can't touch it when I'm done. If MV were increasing, at a 1000yd event, I would have to start taking elevation out of the dope as I progressed and that's not typical. Also that heating invariably leads to flyers with light barrels. That's gun-specific. I do have a couple hunting rifles that climb when they get hot. I also have a 338 Edge which I shot a match with from 1000 to 2000 yards in a manner where the barrel got quite hot, and there was non stringing. I once gave a cheap 22" .243 Savage take-off barrel to a friend, who slapped it on an action and shot a 600yd F-class match with it. That thing was red hot after a 30-shot string (with sighters) but there was less than an MOA vertical dispersion on the target, and no pattern between early and late shots.

 

[jdavistx]

I think this has been an insightful conversation. Let's take it to the next level. If you have a 5% delta in measurement systems with a powder temperature coefficient of 1.2. it's a 1% problem. Are your environmental and MV measurements within 1%?

 

[jdavistx]

I don't.

The issue is irrelevant for hunting rifles, I simply take my time on the range so heating is never an issue as when I hunt the gun will be cold so I want important shots to be representative of that condition. With high powder capacity rounds I'll take 3-5min between shots.

I see a lot of unsubstantiated assumptions in this thread, like barrel temp affecting MV. I shoot F-class and on my first string with unlimited sighters it's typical to put 25-30 rounds of 284Win down range in 15 minutes. Granted it's a 1.25" cylinder barrel but I can't touch it when I'm done. If MV were increasing, at a 1000yd event, I would have to start taking elevation out of the dope as I progressed and that's not typical. Also that heating invariably leads to flyers with light barrels. That's gun-specific. I do have a couple hunting rifles that climb when they get hot. I also have a 338 Edge which I shot a match with from 1000 to 2000 yards in a manner where the barrel got quite hot, and there was non stringing. I once gave a cheap 22" .243 Savage take-off barrel to a friend, who slapped it on an action and shot a 600yd F-class match with it. That thing was red hot after a 30-shot string (with sighters) but there was less than an MOA vertical dispersion on the target, and no pattern between early and late shots.

Yes, hunting is a cold bore shot!

 

[jdavistx]

Yes, hunting is a cold bore shot!

That was my point....

 

[ntsqd]

Yes, hunting is a cold bore shot!

Most times you're doing it wrong if it isn't, but not always. Varmints and depredation hog hunts come to mind as exceptions.

 

[jdavistx]

True. I just don't shoot what I don't eat.

 

[P7M13]

we have no knowledge of the thermal conductivity of steel. How is heat actually traveling through the barrel and how long does it take?

Au contraire! Thermal conductivity, emissivity, coefficient of expansion, shear modulii, to name a few, are all thoroughly studied properties of the numerous alloys of steel. Why? Lives depend on that information.
You could figure it out if you wanted to, the math is pretty fun - though I haven't done it in decades. I do still have a few steel books on my shelf though. Good reference information that you would be hard pressed to find on the internet.
If you *really* wanted to know what was happening with the temperature on your barrel, I'd recommend a thermal camera from Flir. Temperature will affect your accuracy way more in terms of the heat distortion of the steel in your barrel due to thermal gradients and stress profiles. If your barrel was not annealed properly, there will be residual stress that can amplify the distortion of the barrel on heating.
Like most everyone has said, you are *way* overthinking this.
Some suggestions:

1. Take up reloading. You will *really* be able to tune your loads.
2. An SD of 8.5 is good, but that generally means your ES will be in the double digits. Some thoughts on that:
   • Reloading will give you the opportunity to dial that in tighter.
   • As mentioned by Alex Wheeler in another thread, ignition is everything. Four things that can really affect this are primer selection, primer seating, flash hole uniformity and the consistency with which your firing pin strikes the primer. You may see the results of this through single digit ES and SD. BUT, the whole point of that is to turn one variable in the accuracy equation into a constant.
     Trigger time and reading the wind are some of the hardest variables to master.
3. You used the phrase, "what the Pros do...." When I hear that, I hear a person who drinks the Koolaid or is just asking to get fleeced. If you haven't already, join a club, shoot competition, talk to the guys there. Some will be sponsored -- not in some lucrative way like we might imagine, and most will do it for the love of the sport. You will learn oodles just watching them, and even more chatting. Shooting with others gives perspective so you don't loose sight of the forest from the trees.
4. Back to #1, take up reloading. It won't save you money. Shooting, and especially LR, is an expensive hobby/sport. What happens is you will shoot a heckuva lot more, and spend less in the process.
5. [edit to add] Heat affects the reaction rate (burning rate) of gunpowder, which is one reason why many in LR are concerned with temperature sensitivity. It's the ambient temperature that has the most effect because that will be the temperature of your powder in most cases. Unless you chamber a round in a hot barrel and then wait. If you are a deeply skilled shooter, you may see the difference the barrel temperature has on your developed pressure and MV, but in all likelihood, the barrel distortion has a much greater effect.