cfreund@PICA.ARMY.MIL (CCL-L) (01/17/90)
From: "Charles T. Freund" (CCL-L) <cfreund@PICA.ARMY.MIL>
RE: Falling bullets
"Hatcher's Notebook" by Julian S. Hatcher, Major General, USA, RET
Copyright 1962 contains a chapter entitled "Bullets from the Sky" which
details a number experiments concerning the terminal velocity of falling
projectiles. The bottom line is that most .30 caliber bullets will
reach a terminal velocity of about 300 ft/s. Bullets falling point first
will fall faster at first than bullets falling base first, but a 150-
grain .30 caliber bullet tends to balance its weight against air
resistance at a speed not to far from 300 ft/s. Tumbling projectiles
start out falling slower, accelerating at a slower rate, but will level
out at about 300 ft/s.
Translating this, a 150-grain bullet traveling at 300 ft/s
corresponds to about 30 ft-lbs. By Army standards, an average of
60 ft-lbs is required to inflict a disabling wound. Thus, a falling
150-grain .30 caliber bullet is not likely to cause a lethal wound.
Will I stand under a falling bullet to prove this? Not likely!
The lethality of falling projectiles increases drastically for
larger calibers. An ordinary 718-grain .50 caliber machine gun bullets
has a terminal velocity of nearly 500 ft/s and a final energy of just
less than 400 ft-lbs. A 1000 lbs 12-inch shell will reach a speed
between 1300 and 1400 ft/s and over 28,000,000 ft-lbs!
Charles T. Freund <CFREUND@PICA.ARMY.MIL>
US ARMY, Armament, Research,
Development, and Engineering Center
Picatinny Arsenal, NJ 07806-5000jacob@cd.chalmers.se.chalmers.se (Jacob Hallen) (01/20/90)
From: jacob@cd.chalmers.se.chalmers.se (Jacob Hallen) Could people please try to use metric units in their postings. Footpounds and fathoms per fortnight are very difficult to understand for most non-americans. Besides, many of these units are not very well defined or even have multiple definitions. Jacob Hallen [mod.note: There are, of course, obvious exceptions. I can't see the value in referring to a 16" gun as a 406mm, nor do I care to speak of a 2.2-megatonne nuclear warhead. Where practical, though, I encourage writers to use SI units, or dual units. - Bill ]
root@grumbly.UUCP (Super user) (01/22/90)
From: root@grumbly.UUCP (Super user)
How long does it take for a projectile from a rifled barrel to spin
down? Would a bullet fired upward still have spin when it reached the
ground?
--
oo uunet!grumbly!root
) Richard B Ducoty root@GRUMBLY.COM
'~~`< ba Capitola, CA (408) 475-6539 NCF::DUCOTY
humbug 95010-2733gwh%tornado.Berkeley.EDU@ucbvax.Berkeley.EDU (George William Herbert) (01/23/90)
From: gwh%tornado.Berkeley.EDU@ucbvax.Berkeley.EDU (George William Herbert) In article <13382@cbnews.ATT.COM> root@grumbly.UUCP (Super user) writes: > How long does it take for a projectile from a rifled barrel to spin >down? Would a bullet fired upward still have spin when it reached the >ground? iIn normal flight [horizontal] the bullet tends to retain angular momentum longer than linear momentum [slows down faster than spins down]. If you fire it straight up, tho, i bet it will spin down before it comes down...but i bet it's spinning at a third or so its origional rate when it stops rising. **************************************************************************** George William Herbert | UCB Naval Architecture [On schedule? at UCB? Yes!] ---------------------------------------------------------------------------- gwh@ocf.berkeley.edu ||||||||| "And What if I Don't?" "Then, You Die, gwh@soda.berkeley.edu ||||||||||||||| the Girl dies, Everybody Dies..." maniac@garnet.berkeley.edu |||||||||||||||||||||||||||||||||||| -Heavy Metal
ae219dp%prism@gatech.edu (Devon Prichard) (01/24/90)
From: ae219dp%prism@gatech.edu (Devon Prichard) two anecdotes; my roomate's father wasin the German army in WW II. he was in a bomb crater when the Russians put a artillery shell in the crater, right between him and his squad-mate. the fuse didn't blow (otherwise I'd be in a one-bedroom apt. !!) but the shell lay on the dirt spinning like mad _for several minutes_ !! a friend of mine who is a cop, told a story to me about someone firing an AK-47 in a concrete office building (I think it was a stairwell). the bullet ricocheted around until it stopped travelling, but lay on the ground spinning for awhile (making a buzzing noise). a dumb calculation; if the muzzle velocity of a hypothetical bullet is 3000 ft/sec, and the barrel has 1 in 12 twist (1 turn in 12 inches of travel), then, assuming that, for the last foot of travel along the barrel, the bullet is at 3000 fps, the spin rate out of the muzzle would be 15,000 rpm. don't ask me how long the aerodynamic boundary layer would take to dissipate that much rotational energy, because it would require an unsteady analysis, from the time the bullet left the barrel to rest condition (i.e. from supersonic to transonic to subsonic conditions). give me $150K and I'll do it !! -- |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| | Devon Prichard making the world safe for helicopters ... | | ae219dp@prism.gatech.edu | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||