Rule of Thumb for Shooting Down Hill

[Wrenches]

Some real good information posted in this thread.

 

[Stgraves260]

Hi everyone. Got back earlier this week from hunting CO 2nd rifle elk season in GMU 681. Took a cow early on but the bulls were scarce especially given the high winds. At dusk on Weds I had a 5 pt bull appear at 503 yards quartering to and since he was close (30 yds from) a fence (private ranch on the other side), I aimed high on the shoulder (after dialing my Gunwerks 7mm RM shooting 168 gr VLDs to 500 yds) & gently squeezed. My spotter called the shot right over his back. The bull promptly moved off into the timber (not presenting another shot), jumped the fence and minutes later was shot on that private ranch. One more data point, the bull was 10 degrees downhill from me and I had a solid but not perfect rest.

My question is, did I just muff the shot high or should I have dialed a shorter distance on the Viper PST? Do you have a rule of thumb for shooting at high or low angles, like "for 10 degrees, reduce the distance by 10%"?
Thanks for your time & advice!

This may come across pretty brutal, but before you take a shot at a living breathing thing. You need to understand how to shoot in those type of situation. My advice is get some proper training. As a ethical hunter, we want a quick humane kill. As a hunter, we don't spray and pray. Get some proper training and practice on none living targets.

 

[Stgraves260]

@Stgraves260
What does your math show he should have dialed for to be exact? Is it not multiply the yardage by the cosine? If I am correct the yardage hold should have been 495yards or in his instance exactly what he dialed.

What was his LOS and what is his rifle zeroed at? Was a rangefinder used? Did the rangefinder calculate for angle cosine?

 

[jaspepp]

If anyone wants to nerd out on this topic a bit, Joseph von Benedikt had Aaron Davidson on his podcast (Backcountry Hunting) talking about this same topic last week

 

[Stgraves260]

What was his LOS and what is his rifle zeroed at?

What was his LOS and what is his rifle zeroed at? Was a rangefinder used? Did the rangefinder calculate for angle cosine? Did you use a protractor to get the angle? There is so many questions before I can help answer, but I'll try and help.

 

[TRexF16]

What we use for a rule of thumb in archery is aim the horizontal distance. It's probably not perfect but it will keep you in the 12 ring. I would think it would get you really close with a gun also.

Actually, I think it IS perfect. That's exactly the right rule of thumb. Gravity only acts on the bullet or the arrow over the HORIZONTAL component of it's flight path. The 90 degree pure vertical case illustrates this clearly. There is no horizontal component to the slant range from shooter to the target, so there is no "drop", regardless of the slant range. The projectile flies in a perfectly straight line from release to impact with the earth.

Cheers,
Rex

 

[Reelamin]

What was his LOS and what is his rifle zeroed at? Was a rangefinder used? Did the rangefinder calculate for angle cosine?

Is the math formula I used correct?

 

[Stgraves260]

If you know your exact LOS. Do not touch your elevation turret until you get your angle. You can use a protractor w/ some kit string and a fishing weight to get your angle. I have all my rifles zeroed at 100 yards so that I may get better accuracy when calculating angles. So if you know your LOS was 500 yards and your angle was 10 degrees. No matter the distance the cosine for 10 degrees stays the same at .985 cosine. So multiple your cosine of .985 X ( LOS yards ) 500 = 492.5 yards. Another word no hold over or under was needed.

 

[Stgraves260]

Is the math formula I used correct?

Yes. Multiple the yardage by the cosine. To get the correct angle you must leave your rifle in its zero. Put the crosshairs on the target and have your spotter use your protractor to get the proper angle. After you get the proper angle then you can convert your angle to cosine. After that, then you can do the math and start dialing for elevation.

 

[greenejc]

Hi everyone. Got back earlier this week from hunting CO 2nd rifle elk season in GMU 681. Took a cow early on but the bulls were scarce especially given the high winds. At dusk on Weds I had a 5 pt bull appear at 503 yards quartering to and since he was close (30 yds from) a fence (private ranch on the other side), I aimed high on the shoulder (after dialing my Gunwerks 7mm RM shooting 168 gr VLDs to 500 yds) & gently squeezed. My spotter called the shot right over his back. The bull promptly moved off into the timber (not presenting another shot), jumped the fence and minutes later was shot on that private ranch. One more data point, the bull was 10 degrees downhill from me and I had a solid but not perfect rest.

My question is, did I just muff the shot high or should I have dialed a shorter distance on the Viper PST? Do you have a rule of thumb for shooting at high or low angles, like "for 10 degrees, reduce the distance by 10%"?
Thanks for your time & advice!

I got back this week, too. I didn't even see an elk at Crawford. Yes, shooting at an angle means the tragectory will be flatter. Also, altitude will make it flatter at distance. Coupled with the larger group sizes distance gives you just from variations in shot to shot velocity, wind, etc, holding high could easily generate a miss at that range. Good job on the cow. Where were you hunting? I used a 35 Whelen and when I got bored, I shot some practice shots at the elevation I was hunting in, and well away from where I was hunting, using a Shepherd scope and a Bushnell range finder. I knew where my rifle would hit, and the 3 shot group size at 330, 350, 430, 490, 610 and 720 yards at both level and up to 25degrees with the load I was using. Since the elk hadn't come down, there wasn't a reason not to practice under real world conditions. It did scare some deer, though. And since I was alone out there, it didn't mess with anyone else's hunting. I also shot to 1,000 yards, and it was about point of aim with the Sierra Gameking 225 grain loads. But I have shot bowling pins with that load at 300 yards from a bipod at Fort Benning using this rifle/scope combo on several occasions along with golf balls (my son-in-law's) at 100 yards at the Benning POF range.

 

[Reelamin]

Actually, I think it IS perfect. That's exactly the right rule of thumb. Gravity only acts on the bullet or the arrow over the HORIZONTAL component of it's flight path. The 90 degree pure vertical case illustrates this clearly. There is no horizontal component to the slant range from shooter to the target, so there is no "drop", regardless of the slant range. The projectile flies in a perfectly straight line from release to impact with the earth.

Cheers,
Rex

Is a bullet/arrow moving horizontally if it must rise vertically from its starting point to impact its intended POI lower then the peak of its arc. Yes, at enough distance away to matter on perfectly level ground? Is it gravity that causes it to drop after the top of it's arc? I believe the answers are yes. If you take that exact same set up and aim it at a 90 degree angle up or down does that bullet/arrow not follow the same initial rise before dropping as if fired horizontally? Would that movement not still be horizontal movement from its starting location? I think gravity still applies straight up or down it just is pushing directly with or against the bullet/arrow increasing or decreasing its speed and affecting it's horizontal decline less. Would this then not cause as much decline at the top of the arc so the new POI would be higher? I am not a scientist or mathematician, and that is the best way I think I can explain how I got my understanding. Please educate me if I have it wrong before as I am ignorant in more than one topic.

 

[Critter Picker]

Seems odd since bow sights are above the bore/arrow, and the arrow must fly in the same arc pattern to get to the POI. Gravity still applies to an arrow as it does to a bullet. I'm open to learning more if you have the information. I don't shoot a very fast bow 274fps, and mine has always shot noticeably higher at angles above 15 degrees. I dont remember checked the degrees just estimating now, and when I did the testing its very close to a 30 degree angle. It is 5 yards different hold at 40-60 yards.

Try shooting the horizontal distance. I've taught bowhunter education since 94 and the bows back then didn't exactly smoke arrows (we thought they did) . My current set up is only shooting 295 (60 lbs @ 28")

Due to differences in both bow design and anchor point the height of the sight to arrow is a little different for everyone. But horizontal distance works for me. I have a angle compensating range finder and the shoot for range is usually really close to horizontal distance on it.

 

[Stgraves260]

There IS a rule of thumb for for angled shooting. Aim low. For up hill OR down hill. It doesn't matter.

That's the rule if you don't want to get into the weeds.

If you do want to get into the weeds I recommend you get familiar with rifleman's rule, and the improved rifleman's rule. Or you can know none of it, get a kestrel and be sure to know what data to use, and you'll be just as good.

No sir. It does not matter if you shoot up hill or down hill the math stays the exact same. For instance. If your target is at a LOS of 700 yards, and a 45 degree angle. Up hill the math would be. 700 X ( cosine .707 ) = 494.9 yards. So now do the same 700 yards and the same 45 degree angle and you still get a shoot to range of 494.9 yards down hill shot.

 

[Stgraves260]

Is a bullet/arrow moving horizontally if it must rise vertically from its starting point to impact its intended POI lower then the peak of its arc. Yes, at enough distance away to matter on perfectly level ground? Is it gravity that causes it to drop after the top of it's arc? I believe the answers are yes. If you take that exact same set up and aim it at a 90 degree angle up or down does that bullet/arrow not follow the same initial rise before dropping as if fired horizontally? Would that movement not still be horizontal movement from its starting location? I think gravity still applies straight up or down it just is pushing directly with or against the bullet/arrow increasing or decreasing its speed and affecting it's horizontal decline less. Would this then not cause as much decline at the top of the arc so the new POI would be higher? I am not a scientist or mathematician, and that is the best way I think I can explain how I got my understanding. Please educate me if I have it wrong before as I am ignorant in more than one topic.

Your ok. Use that chart I gave you and practice on some none living targets. Set a target out to say 500 yards. Do the best you can and set up a steep angle down hill and up hill shot. Keep in mind, if you see sky in your scope do NOT pull your trigger. Also don't forget about Coriolis effect of shooting East or West. Its not just about angles. It's about direction as well. Now one of my rules of thumbs I use is when I shoot East my bullet impact is high because that is towards Dallas Texas and thing get expensive. When I shoot West towards Mexico my bullet hits low things get cheep when you go West. I dont have anything against Mexico or Dallas. I'm talking from a price point. So when I shoot East I adjust my scope low. When I shoot West I adjust my scope high. Hope this helps.