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 Shooting downhill
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Mgderf
Member

874 Posts

Posted - 03/31/2018 :  2:11:35 PM  Show Profile
O.K. this is kind of a general question.
I have new hunting property that includes the option to shoot downhill.

My new property has a hillside about 80 feet tall and near a 60 degree down angle.
The layout of my property will allow for a 300 yard shot from the top of the hill to the far side of the property below.

I know shooting downhill will change the point of aim/impact, but my question is, how much?
My uncle wants to use his .25-06. I told him I doubt there will be much change, but I'm not sure.
I'll either use a .30-06Springfield, a .243Winchester, or a .308Winchester.

Will there be enough change in the point of impact over a 300 yard range?
If so, will the shot be higher or lower?

I need to take the rifle out and sight it in from my shooting position. I understand that. I'm just trying to save a little set-up time and costs.

Thanks

Have no fear of perfection- you'll never reach it.
"Cogito, Ergo Armatium Sum"- I think, therefore I am armed

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Dormant U.S.Marine
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iceracerx
Advanced Member

USA
8847 Posts

Posted - 03/31/2018 :  2:29:14 PM  Show Profile
http://www.millettsights.com/downloads/shootinguphillanddownhill.pdf

Edit: I tried to find an actual 'angle of the dangle' ballistics calculator but didn't have any luck.

And, you are welcome


Edited by - iceracerx on 03/31/2018 3:51:31 PM
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Mgderf
Member

874 Posts

Posted - 03/31/2018 :  2:44:57 PM  Show Profile
quote:
Originally posted by iceracerx

http://www.millettsights.com/downloads/shootinguphillanddownhill.pdf





OUTSTANDING!
I thought I'd get the info. i needed here.
Hard to believe it came in the first post, and in less than 10 minutes!

Thank you sir.
You just made my life easier.

Have no fear of perfection- you'll never reach it.
"Cogito, Ergo Armatium Sum"- I think, therefore I am armed

NRA Benefactor Life Member
Dormant U.S.Marine
Semper Fidelis
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Mobuck
Advanced Member

11015 Posts

Posted - 03/31/2018 :  7:14:09 PM  Show Profile
The hypotenuse is 300 yards. One of the legs is 80'. Use your handy dandy calculator to figure the other leg--that's the horizontal distance to target which will tell you where your POI will be.

Mobuck<BR>
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Mobuck
Advanced Member

11015 Posts

Posted - 03/31/2018 :  9:25:26 PM  Show Profile
[quote]Originally posted by Mobuck

The hypotenuse is 300 yards. One of the legs is 80'. Use your handy dandy calculator to figure the other leg--that's the horizontal distance to target which will tell you where your POI will be.
If my calculations are close, the difference due to downhill angle will be insignificant.
OH BTW, it's not possible to have a 60* angle corresponding to an 80' difference in altitude @ 300 yards distance.

Mobuck<BR>

Edited by - Mobuck on 03/31/2018 9:28:18 PM
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andrewsw16
Advanced Member

USA
11124 Posts

Posted - 03/31/2018 :  9:56:34 PM  Show Profile
Using the ballistic calculator at Hornady:

https://www.hornady.com/team-hornady/ballistic-calculators/#!/

With a few other parameters of: bullet weight=100gr, MV=3200fps, ballistic coefficient =.393, a calculated downward barrel angle of 5 degrees (that was calculated from a hypotenuse of 300yds and a hill height of 80ft), the ballistic calculator shows that if the rifle was zeroed at 300 yards exactly horizontally, at a -5 degree angle the bullet will hit about 1 tenth of an inch high. So, I wouldn't bother with any sight adjustments.
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spirits
Junior Member

USA
340 Posts

Posted - 04/01/2018 :  10:13:21 AM  Show Profile
Depends on what "level range" you sighted your rifle in for - seems like everyone is assuming 300 yards. Usually, the rifle is sighted in for much less (e.g., 100 yards)- not too many people have access to a 300 yard range. Best to avoid wounding an animal and all the regret that comes with it. Put a target up and shoot and see what happens.
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andrewsw16
Advanced Member

USA
11124 Posts

Posted - 04/01/2018 :  5:19:34 PM  Show Profile
True. I ran it again using the same parameters I entered above, but this time zeroed at 100yds, level, then shot downhill at -5 degrees, at a target at 300yds, the bullet will now hit 9.7 inches low. That would be unacceptable for good hunting, unless you know to expect it and hold over to compensate. So, it looks like the way to get the best hunting reliability and least impact difference is to go ahead and sight in at the expected game distance and level, then trust that a bit of uphill or downhill isn't going to make much PRACTICAL difference for hunting. It sure doesn't hurt to go out and do some practical experiments and make up a laminated dope card and tape it to your stock.
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Mobuck
Advanced Member

11015 Posts

Posted - 04/01/2018 :  6:37:28 PM  Show Profile
"seems like everyone is assuming 300 yards."
Nope, the OP STATED the distance as 300 yards from stand site to property line.
Now, ASSuming the line of sight distance IS 300 yards and the altitude difference IS 80'. The actual horizontal distance is very close to 292.5 yards. That's so close to 300 yards that no noticeable change to the POI would result. Makes no diff what the sight in range is as long as the shooter knows his 300 yard POI.

Mobuck<BR>
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Geri
Senior Member

1219 Posts

Posted - 04/04/2018 :  09:48:42 AM  Show Profile
Cos of the angle. Rule of thumb, 310, 420. Hold about 10"high at 300 yds
20" at 400 yds. Rifle sighted 1" high at 100 yds with scope 2.5" above bore This has worked for me for years. Have a great day to all
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Herschel
Senior Member

2083 Posts

Posted - 04/04/2018 :  5:10:18 PM  Show Profile
If your rifle is zeroed at 300 yards and you take a shot at a 45 degree angle either uphill or downhill at a target 300 yards, gun to target, away you will hit high. The ops question was simple. I don't know how much high but it will be high.

Follow the link provided the second post in this thread to see a good explanation.
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