Hot lead, opinions>

[reddog]

Some background, 380 Auto, hand loads 90gr HP running around 950 fps. Shooting into late 90's chevy truck bed, something the wife keeps telling me needs to leave the yard but anyway, all rounds pass through the side and if they don't go through the far side rebound into the bed. Today getting a little backyard range time I grab the bullets in the bed after a couple of mags and they were hot, almost too hot to hold. So to the question, was the lead hot from the powder burn (I'm thinking no) or from the impact energy?. I'm thinking yes. What do you think?

 

[benenglish]

I always thought it was friction in the bore.

Interesting question. I hope someone has authoritative data.

 

[dee]

I would agree with Ben and also add that there is likely a lot of friction heat added when they punch through the first barrier.

 

[reddog]

I would agree with Ben and also add that there is likely a lot of friction heat added when they punch through the first barrier.

But how much friction could there be punching through a piece of 18 gauge metal? That is why I am thinking the transfer of energy is the cause, the bullet punching through the metal, deforming as it goes through, speed going from 950 fps to zero and heat is generated?

 

[HKSig]

Friction from the air?

 

[cycleguy2300]

Friction from the air?

The heating time is too short t really heat a bullet from air resistant. Even a meteorite will reportedly form frost immediately after crashing to earth and it was moving a whole lot faster for a lot longer, but admittedly started a lot colder too.

To = T*(1 + 0.2*M2)

To= Temp output
T= ambient air temp
M= Mach number

The "To" is the maximum temp at the leading edge and the object would be cooler behind the leading point.

A 22lr or 9mm that travels right about Mach 1 really will not heat much at all over the VERY short ToF. A 7mah or 300WM or 338LM with a long ToF and a high speed may warm a little, but not enough to become thermal stable and would likely not be noticeable.

The heat would be coming from friction of the barrel and a little from the powder burn.




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[G O B]

The bullet will absorb heat from contact with the propellent gas, friction with the barrel, compression on impact, and ANY time it encounters anything hotter than the bullet. It will release heat to anything that it contacts that is cooler.

 

[cycleguy2300]

But how much friction could there be punching through a piece of 18 gauge metal? That is why I am thinking the transfer of energy is the cause, the bullet punching through the metal, deforming as it goes through, speed going from 950 fps to zero and heat is generated?

6g to 300m/s is 270 joules at the muzzle

E= 1/2MV²

So

Joules = 1/2(0.006*300²)
Joules = 1/2 (0.006*90000)
Joules =1/2 (540)
Joules = 270


The energy absorbed by slowing down greatly depends on how it slowed. When tearing a hole in steel the kinetic energy isn't absorbed as heat by the bullet, but by mechanical tearing of the metal (which would release heat, but not significantly into the bullet I wouldn't think.

Incidently, while looking up the specific heat of lead (0.032cal/gram) I saw a problem describing a 300m/s bullet... it assumed an instant deceleration and all energy converted into heat and equally shared between the 0°c bullet and the 0°c target.

At 300m/s a perfect impact and without losing energy to sound etc it would raise the temperature of the 0°c bullet to 167.4°c

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[zackmars]

The bullet will absorb heat from contact with the propellent gas, friction with the barrel, compression on impact, and ANY time it encounters anything hotter than the bullet. It will release heat to anything that it contacts that is cooler.

This.

Propellant heat is the biggest. Smokeless powder burns at over 3,000 degrees, some of that will definitely rub off

 

[Eastexasrick]

6g to 300m/s is 270 joules at the muzzle

E= 1/2MV²

So

Joules = 1/2(0.006*300²)
Joules = 1/2 (0.006*90000)
Joules =1/2 (540)
Joules = 270


The energy absorbed by slowing down greatly depends on how it slowed. When tearing a hole in steel the kinetic energy isn't absorbed as heat by the bullet, but by mechanical tearing of the metal (which would release heat, but not significantly into the bullet I wouldn't think.

Incidently, while looking up the specific heat of lead (0.032cal/gram) I saw a problem describing a 300m/s bullet... it assumed an instant deceleration and all energy converted into heat and equally shared between the 0°c bullet and the 0°c target.

At 300m/s a perfect impact and without losing energy to sound etc it would raise the temperature of the 0°c bullet to 167.4°c

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Our professor in Properties of Materials used to say, math may not solve the initial problem, but it will answer the questions posed by the problem. Darn good example.