Yes, you are probably safe indoors from a straight-up shot.
Outdoors, my Fermi numbers say you could get your skull cracked even in this
(best case) scenario.
[Aside: Wood is, as it happens, a crappy model for human tissue. If you don't believe me,
ask any regular member of the International Wound Ballistics Association.]
A grain is 1/7000 of a pound, IIRC. 150 of those is .01 kg, near enough.
Round 300 fps up to 100 m/s. (1/2)mv^2 gives us 48 kg*m*s^-2, distributed
on the boattail in this case (the round is probably still gyrostabilized).
Bump that down a bit if you want. Now consider:
1) Will the boattail land perfectly flat on your skull? How often? I would guess there
are at least two orders of magnitude possible variation in the contact area. Owie.
2) Most rounds will not be going straight up. This makes a lot of difference.
Commercial and freeware exist for figuring external ballistics. Some is very good,
the best one I know having been done by perfectionist retired SLACers.
3) Then there's secondary effects: broken glass hurting people, causing car
wrecks, etc.
M
hal@finney.org wrote:
> According to http://home.sprynet.com/~frfrog/miscella.htm:
>
> : Hatcher describes one experiment with the 150gr M2 Ball bullet fired
> : vertically. When it came back from vertical (round trip time was about
> : 42.9 seconds) it left only a 1/16 inch dent in a soft pine board that it
> : happened to hit. (Not exactly what it would do at 2700f/s, eh?) Based
> : upon this and similar tests Hatcher concluded that the impact velocity
> : was about 300 f/s, which from additional testing appears to be the
> : terminal velocity (the maximum free fall velocity which is limited by
> : air drag on the body in question) of that bullet falling from any height
> : in the atmosphere. (If I remember correctly from my limited parachuting
> : experience the terminal velocity of a falling person is somewhere around
> : 130 mph or about 200 f/s.)
>
> The article goes on to say that this is fast enough to penetrate the
> skin and potentially cause serious injury. But I doubt that you would
> kill someone hitting them on the top of the head with a bullet going
> only this fast.
>
> Hal
-- Job One: MAKE YOURSELF USEFUL. If you're not part of the solution, what are you doing scumming up the bottom of our beaker? --MMB "Let's roll." --Last words heard over Todd Beamer's cell phone before the counterassault aboard UA93, 02001.09.11.~10:10EDT
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