Re: gun angle

hfs2@xxxxxxxxx wrote:

# I posted this is a couple of sci groups, but they're full of kids.
# Anyone have a empirical answer to this? Here's the post:
#
# If you shoot a 22 rifle straight up, the bullet returns to earth at
# Vv, whatever that is. What is the minimum elevation of the
# rifle to insure that the forward velocity of the bullet, Vh, is
# no greater than (close to) Vv when it hits the ground; a speed
# that doesn't have a good chance of hurting anyone. No
# hills, just level ground all around.


Any object, dropped, will accelerate under gravity until
resistance created by air is great enough to stop further
acceleration. At the top of such an arc, a bullet will
essentially behave as an object dropped with zero starting
velocity. It will accelerate to its terminal velocity
which may depend on air density, that is elevation, temperture,
and air pressure.

I have no idea what that sort of terminal velocity would
be but its far below muzzle velocity.
And it would depend on the aerodynamics
of the bullet. A bullet that is lomng and tumbling
will have more air resistance than a short squat
bullet that tumbles less.

At less than 90 dgrees, such an object will have
forward velocity. A bullet merely dropped and a bullet
fired horizontally will be accelerated by gravity
at the same rate and will hit the ground at the
same time.

Leaving the horizontal velocity of the bullet
to consider. Ignoring gravity, a bullet ceases
to accelerate after it leaves the barrel of a gun.
It starts losing velocity to air resistance.
Eventually air resistance would bring it to a dead halt.

Exactly when depends of the mass X velocity of the bullet,
ambient air temperature and density of air, and the
shape of the bullet, a hollow point bullet will slow
down faster than a spire shaped bullet of same diameter
and weight.

Again it is matter of physics, the main problem being
calculating resistance due to bullet aerodynamics.

A bullet does though eventually hit the ground,
depending on exact elevation, and either the
foward velocity or the gravitationally accelerated
velocity will be greater when it does.

For a low elevation, almost assuredly the bullet's
horizontal velocity will predominate.
For a bullet fired upwards, the vertical gravitational
acceleration will predominate.

So you have a complex series of possibilities depending
on initial conditions, and areodynamics of the bullet
and whether you have a situation the forward velocity
dominates or not.

Again another issue is mass of the bullet.
A .22 LR dropped at 2500 feet will probably not
do much damage, a .50 cal browning bullet will smart.

A bullet still spinning may hit harder than a tumbling
bullet that loses more energy sapped by increased air
resistance.

A 22 hollowpoint will lose a lot more energy fired
horizontally over long distances than a .50 caliber.
A .22 over long enough distance may have little
energy left while a .50 may have more than enough
to be deadly.

There ain't no easy one-size-fits-all answer here.
About the only projectile you can count to lose
enough energy over its usual range to be harmless
are shot gun pellets of small size. Say #4 shot and less.







# With an elevation of zero, the rifle parallel to the ground, I
# suspect Vh is a good percentage of the muzzle velocity when the
# bullet hits.
#
# I just need a general answer to this.
# Be off by xx%? This is not a homework assignment. I know
# that this must be a complicated question, because everyone
# refuses to answer it.... after telling me how smart they are.
# Maybe it can't be answered, maybe it can only be measured.
#
# What info I have. Velocity is around 1,138 fps and the round is
# about 40 grains
#
# Thanks
#
#
--
Happy Hogmanay!

Cheerful Charlie


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