Posted: 3/27/2013 8:46:26 AM EDT
| So tell me, how fast could a standard copper jacketed lead cored bullet travel through our atmosphere at sea level before the friction with the air started melting the projectile. |
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I REALLY don't want to try to show all the calculations typed out, but a simple answer, based on 20C temperature, standard pressure, 55 grain bullet (.202 ballistic coefficient, solid copper projectile), ignoring all kinds of secondary effects, assuming a travel of 100 meters, and rounding off just about everywhere, 3162 meters/sec., or 10,374 feet per second) is a not-so-wild guess/back of envelope calculation. ETA: this is for solid copper, I don't want to think about copper clad - would need cladding thickness, etc.  |
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Quoted:
How much energy is contained in a 55gr round traveling that fast? E=MC^2 I hate to go all Einstein on you, but that's the equasion. Energy equals mass times the speed of light squared. Just take the speed of light at 186,000 miles a second and extrapolate that down to the required speed and multiply from there. |
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How much energy is contained in a 55gr round traveling that fast? E=MC^2 I hate to go all Einstein on you, but that's the equasion. Energy equals mass times the speed of light squared. Just take the speed of light at 186,000 miles a second and extrapolate that down to the required speed and multiply from there. LOL, you fail in application of physics. |
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Quoted:
How much energy is contained in a 55gr round traveling that fast? E=MC^2 I hate to go all Einstein on you, but that's the equasion. Energy equals mass times the speed of light squared. Just take the speed of light at 186,000 miles a second and extrapolate that down to the required speed and multiply from there. Also depends if you're shooting eastward or westward. Don't forget the rotation of the earth. You gotta break out some trig if you're shooting anywhere in between straight east or straight west. |
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In reality I wouldn't be surprised if the bullet fragmented well before reaching meltdown speed. Air starts getting pretty thick at that speed. Actually, it would be spinning so fast as to probably fly apart. I know the lighter bullets do it when pushed much over 4kfps |
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was going to post this in reply to the E=MC^2 post... Quoted:
kinetic energy E=1/2*mass*v^2, so E = 0.5*(3.5x10^-3 kg)* (3162 m/s ^2) E ~ 17,500 Newton meter In foot-pounds -> ~ 12900. That's only the translational energy. What about rotational energy? This is why energy is not a good account of wounding ability. Also, it's interesting that aprox 10k fps is enough to degrade the bullet. I would have thought it would take more than that but I'm no physicist. |
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So,, extrapolating on this post, it there were a space shuttle door gunner, and he dumped 200 rounds from his chain gun toward the earth, would there be a condensed meteor shower show on the ground?
(Bullets should be well above that speed when they hit the atmosphere) |
| Correct me if I'm wrong, but wouldn't this have something to do with specific heat of copper and air? The heat from the friction can't really conduct to the copper enought to melt it in the few seconds that the bullet is in the air or at speeds that produce thay kind of friction. Same reason pans take time to heat up and you can touch a fire really quickly with out getting burnt. |
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Quoted:
Quoted:
Quoted:
How much energy is contained in a 55gr round traveling that fast? E=MC^2 I hate to go all Einstein on you, but that's the equasion. Energy equals mass times the speed of light squared. Just take the speed of light at 186,000 miles a second and extrapolate that down to the required speed and multiply from there. LOL, you fail in application of physics. |
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Quoted: Correct me if I'm wrong, but wouldn't this have something to do with specific heat of copper and air? The heat from the friction can't really conduct to the copper enought to melt it in the few seconds that the bullet is in the air or at speeds that produce thay kind of friction. Same reason pans take time to heat up and you can touch a fire really quickly with out getting burnt. That's why I assumed a bullet travel distance of 100 meters, and then calculated for the required temperature change to get the copper to melting temp (1085C). |
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I REALLY don't want to try to show all the calculations typed out, but a simple answer, based on 20C temperature, standard pressure, 55 grain bullet (.202 ballistic coefficient, solid copper projectile), ignoring all kinds of secondary effects, assuming a travel of 100 meters, and rounding off just about everywhere, 3162 meters/sec., or 10,374 feet per second) is a not-so-wild guess/back of envelope calculation. ETA: this is for solid copper, I don't want to think about copper clad - would need cladding thickness, etc. He got her # too!! 
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How much energy is contained in a 55gr round traveling that fast? E=MC^2 I hate to go all Einstein on you, but that's the equasion. Energy equals mass times the speed of light squared. Just take the speed of light at 186,000 miles a second and extrapolate that down to the required speed and multiply from there. LOL, you fail in application of physics. Fail is a little understated. 
A long time ago I took a course in aerothermochemistry. It was harder than E=mc^2. Anyway, someone (else) can do a quick estimate by comparing the stagnation temperature to the melting temp of copper. |