Bullet temp in flight

[RockyMtnMT]

So I geeked out a bit this morning. I'm pretty sure this was beat up pretty good a few years ago when the heat resistant tips hit the market. I did a search for bullet temperature in flight and found this study.

Temperature Measurement of a Bullet in Flight

This study answers a primary question concerning how the temperature changes during the flight of a bullet. To answer the question, the authors performed unique research to measure the initial temperatures of bullet surfaces and applied it to four kinds ...

www.ncbi.nlm.nih.gov

Pretty long read, but the short, farm boy interpretation is, bullets show the highest temp near the muzzle and then cool down in flight. The baring surface showed the highest temp and the meplat and base showed cooler temps. The highest temp they recorded was about 85*C ave from 38 special. The high velocity the tested were 7.62x39 and 308win. Peak temp for these was 63*C and 67*C respectively.

Then I looked up the melting temp for plastic. Given there is lots of different plastics it varies, but the given temp for lowest was 100*C. Harder plastics look to be over 200*C.

According to this test, there was no previous test that actually measured temp in flight. Previous data was theoretical.

I'm done geeking now. Anyone know of info showing bullets running hotter?

 

[deadidarren]

None of this surprised me in the slightest always knew the eldm tip with a load of BS they just used it as an excuse to up the price with a subtle colour change although the bullet does have a Shockwave in front of it while supersonic I believe that would be a hell of a lot more than 80 odd degrees but when you look at time of flight 200 degrees for 1.8 seconds don't believe it's going to do much to a piece of plastic

 

[orkan]

Pretty disappointing that their "fastest" tested, was some of the slowest rifle cartridges available. lol


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[RockyMtnMT]

Pretty disappointing that their "fastest" tested, was some of the slowest rifle cartridges available. lol


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That's why I asked if anyone knew if anything else. I can't read through another study! The fastest they did was 900 m/s. About 3000 fps.

 

[Doom2]

The tip of the bullet is exposed to a total air temperature at the tip based on the bullet Mach number. Assuming a 70 deg F ambient temperature at a Mach number of 2 the temperature of the air will be ~500 deg F and at Mach 3 it ~1000 degrees F. The tip bing plastic will not transfer the heat effectivly from the tip. Given time the tip will soften.

The paper referenced is not applicable as it deals with heating of a metallic bullet with a high heat capacity.

Edit: https://www.grc.nasa.gov/WWW/BGH/stagtmp.html

 

[RockyMtnMT]

The tip of the bullet is exposed to a total air temperature at the tip based on the bullet Mach number. Assuming a 70 deg F ambient temperature at a Mach number of 2 the temperature of the air will be ~500 deg F and at Mach 3 it ~1000 degrees F. The tip bing plastic will not transfer the heat effectivly from the tip. Given time the tip will soften.

The paper referenced is not applicable as it deals with heating of a metallic bullet with a high heat capacity.

Edit: https://www.grc.nasa.gov/WWW/BGH/stagtmp.html

I read it, but not well. My ability to geek out is low right now! How did they measure temp in the flying object? It doesn't look like they were testing bullets, but aircraft? I think in the study I posted they reported that the highest temp was close to the muzzle and it became lower through the trajectory. Lowering about 9*C.

 

[Doom2]

The physics is the same. There are other papers available on the internet. Back when spaceflight was in its infancy one of the major hurdles that had to be overcome was how to get a satellite/capsule back from space without burning up. It was decided to use a blunt object with a sacrificial surface to remove the heat away from the capsule. The energy of the moving object is imparted into the air in front of the bullet and raises the the temperature of the air.

In your paper they were trying to measure bullet temperature not temperature of the air in front of the bullet. The bullet has significant mass and a high heat capacity (takes a lot of heat and time) to raise the temperature. In the case of a plastic tip, it does not have much mass, doesn't conduct heat well, and the point will deform at low temperatures.

The theory behind what is happening involves the principles of thermodynamics, heat transfer, and fluid mechanics. I plotted the Stagnation Temperature vs Mach number assuming a 70 deg F ambient temperature.

I hope this helps.

 

[RockyMtnMT]

The physics is the same. There are other papers available on the internet. Back when spaceflight was in its infancy one of the major hurdles that had to be overcome was how to get a satellite/capsule back from space without burning up. It was decided to use a blunt object with a sacrificial surface to remove the heat away from the capsule. The energy of the moving object is imparted into the air in front of the bullet and raises the the temperature of the air.

In your paper they were trying to measure bullet temperature not temperature of the air in front of the bullet. The bullet has significant mass and a high heat capacity (takes a lot of heat and time) to raise the temperature. In the case of a plastic tip, it does not have much mass, doesn't conduct heat well, and the point will deform at low temperatures.

The theory behind what is happening involves the principles of thermodynamics, heat transfer, and fluid mechanics. I plotted the Stagnation Temperature vs Mach number assuming a 70 deg F ambient temperature.

View attachment 404119

I hope this helps.

If the bullet starts at mach 3, and then continuously slows, does that change things? How does time of flight figure in? Is the bullet instantly 900*f? If that was the case, I would ignite a box of newspaper when catching bullets. I believe combustion point of paper is a bit south of 500*f.

Sorry for all the questions. Trying to wrap my head around it.

 

[memtb]

I'm not sure of the temperature of fired bullets, but I can tell you this….some get pretty darn hot. Not sure if it's from bore friction, air friction (a 100 yard shot) or impact on the media from which it was recovered. This I can say…..if you quickly recover one, and put it in your pants pocket…..you can't get it out of your pocket as fast as you want too! memtb

 

[Nevrsummr]

Im happy to see you are thinking about tips!

 

[RockyMtnMT]

Im happy to see you are thinking about tips!

Haha! I saw a post talking about aluminum tips not having melting issues like plastic tips.

 

[74honker]

I'm guessing opening pandoras box here but would bullet shape and construction also have drastic affects on this. A solid bullet vs C&C that is made with more than one alloy with different heating and tranfer rates. Would think that a solid such as Hammer would have either an advantage or disadvantage delending on which direction the pendulum swings on that. I would think advantage??

 

[Doom2]

The bullet and tip take time to heat up which is what Hornady claims to have found It was a long range phenomena. It is the air that approaches the stagnation temperature not the bullet. The air has to transfer the heat to the the bullet. It takes time and it also depends on how close the shock wave is to the nose. The bullet itself would take a lot longer to see appreciable heating.

As for the bullet or air igniting the paper, there is very little total air being brought to to that temperature.

As for understanding all of this it can be difficult. After World War II there was a tremendous amount of research into trying to understand how objects behave as they approach sonic velocity (Mach 1) and beyond. This included the behaivor of shock waves, aerodynamic heating, and their effect on aircraft and missile design. Truly understanding all of this falls into the realm of aeronautical and aerospace engineering.

 

[RockyMtnMT]

As for understanding all of this it can be difficult. After World War II there was a tremendous amount of research into trying to understand how objects behave as they approach sonic velocity (Mach 1) and beyond. This included the behaivor of shock waves, aerodynamic heating, and their effect on aircraft and missile design. Truly understanding all of this falls into the realm of aeronautical and aerospace engineering.

Totally agree. I'm not sure there is an understanding when it comes to bullets.