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Re: [Phys-l] Final velocity of bullets



Sorry, I claim a slow IMAP.

bc, who did read new mail just before posting his tumbling question.

Scott Goelzer wrote:

I too learned that bullets spun much faster than I would have guessed. I pose this questions:

When will a bullet start to tumble? Out of my league to solve this.

Given that a pure vertical shot is unlikely, but a high angle is, will the bullet precess as a spiraled football pass does keeping its long axis tangent to the trajectory? <http://footballphysics.utk.edu/ tilt.htm>

Is it possible that under some conditions that the bullet remains spinning but not tumbling thereby reaching a much higher T.V. as it comes in nose first? Considering frontal area alone maybe 5X faster?


Also, if a slow tumbling bullet hits a person and causes little or no damage:
1) would they report it?
2) in the dark and noise of party, would they even know they have been shot?

Are all known cases of falling bullet injuries exceptions rather than the general rule. (same idea as cars exploding during wrecks - only those exceptional cases make the news so it is mistakenly thought to be a common occurrence)

Scott




**********************************
Scott Goelzer
Physics Teacher
Coe-Brown Northwood Academy
Northwood NH 03261
603-942-5531e218
sgoelzer@coebrownacademy.com
**********************************


On Jan 24, 2007, at 8:26 AM, B. Esser wrote:


On Tue, 23 Jan 2007, Quist, Oren wrote:


Of course a rifle bullet is spinning as well as translating. For the
sake of argument, suppose the bullet spins two revolutions as it moves
through a 75 cm long barrel. (these numbers are somewhat arbitrary, but
reasonably close to actual -- please replace with better numbers if you
have them).

Is the bullet still spinning when it reaches its maximum height?

It has been a few years since I participated in high power rifle matches.
Spin rates for these target rifles varied between 100,000 and 300,000 rpm
as measured at the muzzle. While there were various calculations for
minimum spin rates to establish stability, most competitors used a more
empirical method.
In my experience I never saw a tumbling bullet even at 1,000 yard targets.
The holes in the target were circular. An occasional bounced bullet would
leave an interesting non circular hole. Of course launch angle was less than 5
degrees and time of flight was less than a second.
Some real bullet data using my chronograph:
30-06 (bullet diameter of .308 inches), bullet weight 150 grains, muzzle
velocity 2932 fps, velocity at 200 yards was 2,318 fps. This was the
average of 25 shots. There was no wind, temp at 76 farenheit. While I did
not measure the actual spin rate for these bullets (Hornady) other
measurements with identical barrels (twist rate/length) measured muzzle
spin at 158,000 rpm.


--
Bruce Esser
Physics Teacher
Marian High School
http://marian.creighton.edu/~besser

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Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l