Long Range Hunting Online Magazine Slope/Angle ballistics (again!)
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# Slope/Angle ballistics (again!)

#8
02-22-2002, 10:53 PM
 Silver Member Join Date: Nov 2001 Location: tennessee Posts: 480
Re: Slope/Angle ballistics (again!)

This is extremly easy but just in case I'll put it laymen terms. Here's an example
You range a target at 1200yds.The slant angle is 30 deg. The cosine facter for 30 deg. is .8660.
Take the slope angle, .8660 times it by true range(1200yds) and you get 1039yds this is your slant range.This is how much the bullet will drop because of gravity.But rember your windage data will still be based on 1200yds because the bullet has to travel through 1200yds of air.
Any time you can lower your MOA setting your in a gain position. The nice thing about sloped shots is it gives you some leeway on your range estimation, it increases your danger space.It gives you more margin of error for first round hits.

[ 02-22-2002: Message edited by: SEALSNIPER ]
#9
02-23-2002, 07:16 AM
 Platinum Member Join Date: May 2001 Posts: 2,369
Re: Slope/Angle ballistics (again!)

SealSniper

This is extremly easy but just in case I'll put it laymen terms. Here's an example
You range a target at 1200yds.The slant angle is 30 deg. The cosine facter for 30 deg. is .8660.
Take the slope angle, .8660 times it by true range(1200yds) and you get 1039yds this is your slant range.This is how much the bullet will drop because of gravity.

Initially I thought this was all there was to it also but there's more to consider. We know the "gravity" distance is 1039 yards but the distance the bullet must travel is actually 1200 yards, an additional 161 yards.
This 161 yards takes some amount of time and as a result the bullet slows down due to drag. So even though the gravity distance is 1039 yards the bullet is in flight for the amount of time a 1200 yards shot takes. It's muzzle velocity is the same no matter the distance of the shot, the "terminal" velocity is different for the angled shot.

The amount of drop is more than the straight 1039 yards but less than the 1200 yards. The actual amount is still a bit of a mystery for me.

But rember your windage data will still be based on 1200yds because the bullet has to travel through 1200yds of air.

This is sometimes a forgotten consideration.

Any time you can lower your MOA setting your in a gain position. The nice thing about sloped shots is it gives you some leeway on your range estimation, it increases your danger space.It gives you more margin of error for first round hits.

Thinking about "danger space" is a good thing, I consider this on nearly all shots. It's a good bit different for a short vertical target as hunters see and also for a chest & head only for military. (Sometimes I'm quite sure there's a God as he proaects the animals by making them more horizonal then vertical. [img]images/icons/smile.gif[/img] )
#10
02-23-2002, 03:06 PM
 Silver Member Join Date: Nov 2001 Location: tennessee Posts: 480
Re: Slope/Angle ballistics (again!)

DAVE, I dont have the tables with me but I think I remember most of it.I didn't put this in at first because it gets a little complicated(for most).Theres three other things you have to account for -TEMP-BP-AMMO TEMP.First you will need a scientific calculater.
Where going to use my gun.
30cal 220gr BC .640 MV 2820 sighted in at 100yds in starderd condtions.
For BP if its up-multiple by constant,if down divide.
For temp if its up divide by constant,if down multiply.
Here's the shot 1200yds,30 deg. angle,BP 27.55,temp 84 deg.,ammo temp 84 deg.
First we find the slant range 30cos*1200yds=1039
Then the diff. in BP. 1.980. the constant for 1200yds is 1.0367 (I think)
enter 37.4 divide by 1.0367 hit "xy" key enter 1.980(the diff. in BP) hit =34.82398 this goes where BP is on the table.

find the diff. in temp. 25deg. the constant for 1200y is 1.03426
enter 37.4 hit divide enter 1.03426 hit "xy" key enter the diff. in temp (here you move the the decimal point to the left) 2.5 hit =34.37931 this goes in temp on table.

find the diff. in ammo temp. 14deg. the general rule of thumb is +/- 1MOA for every 50fps. diff. in temp. where going to use -.25MOA this goes in the ammo temp table.

Remember that you use the TRUE RANGE for all calculations.After you get EACH new MOA elevation setting subtract EACH one of them from your intial setting,and put them in the space labled DIFF.

INT.MOA SETTING DIFF.
TRUE RANGE 1200y 37.4MOA
SLANT RANGE 1039y 29.3MOA
BP 27.55 34.82398MOA -2.57602MOA
TEMP 84 34.37931MOA -3.02069MOA
AMMO TEMP 84 25deg change -.25MOA

Add all the differences up and subtract or add them to the SLANT RANGE moa setting.Here it comes to 23.45329MOA THIS THE REAL SETTING YOU PUT ON THE SCOPE.This is the setting you would use.

WHEW [img]images/icons/shocked.gif[/img] I know this was kind of long and its not exact because I dont have the tables with me,but its close.The bullet does have to fly through 1200yds. of air.This is how we account for it.
For everybody that wants first round hits at longrange,past 800yds or so YOU MUST MAKE THESE CORRECTIONS!!!!!

SINCERLY THE GRIM REAPER...

[ 02-23-2002: Message edited by: SEALSNIPER ]

[ 02-24-2002: Message edited by: SEALSNIPER ]
#11
02-23-2002, 07:35 PM
 Platinum Member Join Date: Jun 2001 Location: Palmer, Alaska Posts: 2,539
Re: Slope/Angle ballistics (again!)

Thanks Dave,
I have a few more questions but later.

Sealsniper,
You came up with 23.5 MOA corrected for 1200yds?

My programs, both the Oehler Ballistic Explorer and Load From A Disk indicate a larger total drop of 29.3 MOA, and 30.37 MOA respectivly at 1200y with your conditions entered.

At standard conditions with 30° angle also are 32.5 MOA.

1039y drop was 28.1 MOA and 27.2 MOA at your conditions on flat land which does not equal the 23.5 MOA. As Dave suggested it falls somewhere in between the base distance and actual one.

I have some questions about the constants for BP and temp etc but I have to run now.

Later
Brent

[ 02-23-2002: Message edited by: Brent ]
__________________
Brent Moffitt
#12
02-24-2002, 03:03 PM
 Silver Member Join Date: Nov 2001 Location: tennessee Posts: 480
Re: Slope/Angle ballistics (again!)

Brent,I dont guess you caught it in the last post but I said that I didn't have the tables with me.Your right,the right setting would be 27.9MOA,as per JBN ballistics.Thats with out accounting for ammo temp.Putting the ammo temp in it should be 27.75MOA.(I origenily said .25 MOA for ammo temp but it will be more like .8MOA).
My spotter has the tables with him,although I should get them back by the end of the week.When I do I will put what it should be,acording to them.
As for the bullet having a longer TOF. between the two ranges,yes but we have used these tables out to 1100yds and they have worked,even on sloped shots.I've been trying to figure it out but cant so I will ask and see if a few people I know can help.
#13
02-27-2002, 05:12 PM
 Junior Member Join Date: Feb 2002 Posts: 24
Re: Slope/Angle ballistics (again!)

Here are some formulas that may help out.

Drop = -1/2g*t2 or drop is equal to one half constant of gravity times time squared.

So in slope fire we are looking for the component of gravity at said angle.

slope drop = -1/2g*cos Angle * t2 or one half constant of gravity times the cosine of the slant angle times time squared.

The easy way to figure this is to take the drop for level fire at said range and multiply by the cosine of the slope angle. This will give the drop for slope fire.

We are assuming time of flight is the same so no problems there. We are using the actual range so we don't have problems with energy and remaining velocity either.

I hope this helped a little.

Greg
ps.
If you use the formula above for drop you will get a little more drop than shown in most tables and programs especially at longer ranges.
To keep it simple I didn't include the drag component which at longer ranges the drag vector tips up and acts against gravity. This function is built into most tables and programs so I just use the drop inches at range multiplied by the cosine of the slope angle.
Greg

[ 02-27-2002: Message edited by: shootinlong ]
#14
02-28-2002, 05:35 AM
 Platinum Member Join Date: May 2001 Posts: 2,369
Re: Slope/Angle ballistics (again!)

Greg

"The easy way to figure this is to take the drop for level fire at said range and multiply by the cosine of the slope angle. This will give the drop for slope fire."

This is what I assumed was correct after giving the problem some thought.

Thanks for the reassurance.

/r

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