What's Your answer to this Question?
Walt Heitz
myself just the other night and would like to know better how to
compensate. If I'm sighted in at 100 yds., using the ballistics table
supplied by the manufacturer, how would I know what figure to use for
uphill or downhill shots of the same distance."
Well, guess this is a test to see if I still remember trig/geometry from high
school (about 45 years ago).
To answer your question, it depends upon how steep the hill is.
The distance which is important in determining bullet impact is the
horizontal distance from you to a point directly above or below your target.
Once you know this horizontal distance, you use your known trajectory for
this horizontal distance to determine bullet impact (when shooting up or down
hill). This horizontal distance (unless shooting straight up) will always be
less than the actual distance up to or down to your target. In other words,
the actual distance to your target up a steep hill might be 200 yards but the
horizontal distance might only be 126 yards. You would then use the
ballistics for 126 yards.
To calculate the horizontal distance (X), you must know two things: 1) the
actual distance (y) from you to your target (in the example above, the 200
yards) and 2) the angle between the horizontal line and the line to your
target (for example it would be about a 51 degree angle). Then, you can
calculate: the horizontal distance X=y times the cosine of the angle. X=200
yards times cos 51 degrees = 200 times .629 = 125.8 yards.
This is probably more complicated that you wanted, but it is the way to
calculate it (If I remember correctly). And, you would either need a small
calculator with trig. functions or a table of cosine values with you.
A simpler way:
For the following angles, the horizontal distance will be the actual distance
(from you to the target) times the factor given next to the angle:
0 degrees - 1.0 (this means that you are shooting horizontally/no
correction)
20 degrees - .94
30 degrees - .87
40 degrees - .77
45 degrees - .71
50 degrees - .64
60 degrees - .50
75 degrees - .21
90 degrees - .00 (too steep to hunt!)
Thus, as an example, if you were looking up a very steep hill of 60 degrees
and you estimated the distance between you and the target to be 200 yards,
you would use (.5 times 200 = 100) or the ballistics for a 100 yard
horizontal shot.
Hope this helps.
ridg...@voicenet.not.com
wrote:
(snipped)
>90 degrees - .00 (too steep to hunt!)
>
>Thus, as an example, if you were looking up a very steep hill of 60 degrees
>and you estimated the distance between you and the target to be 200 yards,
>you would use (.5 times 200 = 100) or the ballistics for a 100 yard
>horizontal shot.
>
>Hope this helps.
Thanks very much! This is exactly what I needed and can understand
perfectly now. This whole thing was a very good explanation. Thanks
again.
Michael P. Brininstool
>
> On Wed, 28 Aug 2002 17:46:34 -0400, Walt Heitz <BSWH...@aol.com>
> wrote:
>
> (snipped)
> >
> >Thus, as an example, if you were looking up a very steep hill of 60 degrees
> >and you estimated the distance between you and the target to be 200 yards,
> >you would use (.5 times 200 = 100) or the ballistics for a 100 yard
> >horizontal shot.
> >
> >Hope this helps.
>
> perfectly now. This whole thing was a very good explanation. Thanks
> again.
Too bad he is incorrect. You compute the drop for a 200yd shot in MOA and
take sin(angle) times the MOA drop at 200yds, and that will give you the
"apparent" drop in MOA for firing at "angle". SO, if the drop in 3 inches
at 200 yds, and you are shooting upwards at 60 degrees (way to steep) then
the drop will still be 3 inches, BUT, 3 inches straight downwards. The drop
apparent to the person shooting will be sin(60)*3 which is 1.5 inches. So
your aim is (3-1.5)=1.5
inches too high.
A more realistic angle would be 30 degrees, so at 200 yds, 3 inch drop
(but sighted in for 200 yds), then the drop is still 3 inches, but the
portion of that perpendicular to the line of sight in sin(30)*3 which
is (3*sqrt(3))/2 or about 2.5 inches, so you would be about 1/2 inch
high. You would need to aim 1/2 inch below where you want to hit.
This all changes based on sighted range, the range you are shooting,
etc....
--
Michael P. Brininstool mik...@hoplite.org
"I thoroughly disapprove of duels. If a man should challenge me,
I would take him kindly and forgivingly by the hand and lead him
to a quiet place and kill him." -- Mark Twain
Abernathey Family
for 200yds. Gravity's effect on the bullet's path is the same.
Cliff Howard/IPD Services
news:3D6F7F2C...@aracnet.com...
> If the distance is 200yds, whether it is 60 degree slope or level, aim
> for 200yds. Gravity's effect on the bullet's path is the same.
The distance is actually shorter gravity effect wise.......at 200yds and a
60 degree slope a nicely aimed shot just may sail right over the back of
your target depending on rifle ballistics. A 200 yard target at 60 degrees
inclination from horizontal (pretty durn steep!) is actually closer to 120
yards in the amount of gravitational pull that is exerted.
Cliff
ipds.net
Michael P. Brininstool
>
> If the distance is 200yds, whether it is 60 degree slope or level, aim
> for 200yds. Gravity's effect on the bullet's path is the same.
It is actually TIME of flight that matters, not distance. The bullet's
path is NOT the same. Look at it this way: Shooting at a target level
with the shooter, the bore line will actually be pointing upward at
a slight angle. Assuming a 200 yds zero where the bullet hits after
passing through and above the line of sight and then coming back down
(chances are this is the way it would be for a 200 yd zero). That slight
angle will be ABOUT 1 arc-minute or 1/60th of a degree. As the angle
of the line of sight increases, so will the bore-line, and at the same
rate, but the boreline will alway be about 1/60th of a degree higher
than the line of sight. When the line-of sight is 89 degrees 59 minutes
and 30 seconds above the horizontal the boreline will be 90 degrees, 0
minutes and 30 seconds. This means that you will LOOK nearly vertical,
and the bullet will actually travel the other side of vertical and the
gravity will pull the bullet further away from the line of sight, and
the flight path will NEVER re-intersect the line of sight. Also, if the
line of sight is 89 degrees 59 minutes and 0 seconds above the horizon,
the boreline will be exactly vertical. You fire, and the bullet will go
straight up and straight back down, and also not re-intersect the line of
sight again. These both prove that the angle you shoot DOES affect the
impact point versus aim point. I know that I explained the extreme case,
but apparently it was needed to point it out.
--
Michael P. Brininstool mik...@hoplite.org
Never ask a man if he's from Texas. If he is, he'll tell
you on his own. If he ain't, no need to embarrass him.
pappa
is a bunch of hog wash !!!! By the time you get through figuring all
that out the game will be gone.
The truth is , both up hill and down hill shots make people TEND to
shoot high ,
If your gun is on , hold a couple inches low and touch it off ! And if
you have any doubt , don't shoot .
Abernathey Family
>
> "Abernathey Family" <fam...@aracnet.com> wrote in message
> news:3D6F7F2C...@aracnet.com...
> > for 200yds. Gravity's effect on the bullet's path is the same.
>
Wrong. 200yds is 200yds is 200yds. The bullet still has to travel
200yds. The flight time will be that for 200yds. Gravity is all over the
place and it works even on an angle.
Michael P. Brininstool
Exactly! That was my point! Try reading what I said. The previous
posters were saying the horizontal distance is what affects the bullet
drop, and I was saying that what mattered is TIME in Flight. 200 yds
up or down or horizontal is vastly different horizontal flight
distances, the same actual distance, and only slightly different
flight times.
The drop will be roughly 3 inches VERTICAL. The sights do not
show you vertical drop, they show you an angle that is close
to perpendicular to the line of sight. Do I need to draw a
picture?
--
Michael P. Brininstool mik...@hoplite.org
"Clinton did more than any recent president to place the federal
government above all laws - above the Constitution - and beyond any
effective restraint." -- James Bovard, chapter 19, "Feeling Your Pain:
The Explosion and Abuse of Government Power in the Clinton-Gore Years"
Michael P. Brininstool
You do the figuring in advance so that when the real-world situation
comes up, you have an idea of how high you will be. How is one to know
if it is a matter of inches or feet or centimeters without the
pre-calculations done. I agree that for 1-200 yds, it probably does
not matter much, but if you are shooting at 400-1000 yds, it matters
a LOT!
--
Michael P. Brininstool mik...@hoplite.org
"To announce that there must be no criticism of the president, or that
we are to stand by the president right or wrong, is not only unpatriotic
and servile, but is morally treasonable to the American public."
-- Teddy Roosevelt
Cliff Howard/IPD Services
> Cliff Howard/IPD Services wrote:
> >
> > "Abernathey Family" <fam...@aracnet.com> wrote in message
> > news:3D6F7F2C...@aracnet.com...
> > > If the distance is 200yds, whether it is 60 degree slope or level, aim
> > > for 200yds. Gravity's effect on the bullet's path is the same.
> >
> > The distance is actually shorter gravity effect wise.
> --snip--
> Wrong. 200yds is 200yds is 200yds. The bullet still has to travel
> 200yds. The flight time will be that for 200yds. Gravity is all over the
> place and it works even on an angle.
Yes but it doesn't work near as well on an "angle"....... as far a gravity
is concerned your 200 yards is a lot less. You cannot argue with physics.
Flight time will be the same or very close, the effects of gravity will not
be.....sure as heck don't take my advice go out in the hills and try it. Set
up two targets, sight in at a level 200 yards then move the target to a
point 60 degrees above level 200 yards away. Same sight point you will be
lucky to hit anywhere near the paper......
Cliff
mark
drop distance ( the total bullet drop from the muzzle NOT the scope
drop).
The bullet still travels the same amount of time, and time tells us
how far a body falls due to gravity. D = 1/2 A( T*T ),
where D is the total distance fallen, A is acceleration due to gravity
and T is time in seconds.
You need to know the bullet drop at the distance you are shooting, and
multiply THAT(drop) number by:
5 * .004 d (drop ) = the new drop at this distance
10 .015
15 .034
20 .060
25 .094
30 .134
35 .181
40 .234
45 .293
50 .357
55 .426
60 .500
Degrees up/down
If you are sighted in @ 200 yards with a .270 @3000 fps and a B.C. of,
Your total bullet drop at 400 at yards is 37.56 inches .
IF your target is 400 yards away BUT up or downhill 30 degrees you
multipy the drop at 400 yards (37.56) times ( .134 ) = 5.03 inches.
At 400 yards ( on LEVEL ground )the bullet would be 19.47 inches
below the rifles line of sight to which you must subtract the 5.03
inces.
You would compensate 14.44 inches (19.47 - 5.03) instead.
( FROM SIERRA BULLETS LOADING MANUAL)
good shooting,
edge.
pappa
at 400 to 1000 yards much less at an angle! I know I'm certainly not one
of those people and I was born and raised hunting in long shot country.
Maybe 400 + is ok for varmits , where you either hit or miss : but
with big game I'm betting more game has been wounded and called a miss ,
than dropped in their tracks.
Now I'm betting that there will be 3 or 4 people that will claim to
make 400 yard shots ALL the time. Yeah maybe at the bench with bags or a
vise but not in the field.
I'll be interested in hearing these stories !
Michael P. Brininstool
I didn't mean to imply that hunting at 400m plus was usual. I was
trying to point out where bullet drop on a slope could be enough
to make you miss if you did not have a pretty good idea how to
adjust your aim. The same will apply for a shorter range and
smaller target. being off by 6 inches could be a miss.