How close is the cosign rule in slope shooting?

newtonian

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Jul 30, 2013
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33
There are a couple common methods used, with varying accuracy.
  • Rifleman's Rule. Seems more common, but it not very accurate. Shooter gets MOA values from their 0-inclination range card for the horizontal distance range.
  • Improved Rifleman's Rule. What Dog Rocket explained. This method is surprisingly accurate, and imo is easier to do. Shooter multiplies the drop MOA values from their 0-inclination range card by the cosine(shooting angle).
-For both cases, use the wind values for the line-of-sight range with no correction factor
-If you want to convert your hold MOA to inches of drop, you have to use the horizontal distance to do so.

I went through this whole analysis last week as I became curious after some discussion in another thread. I was not surprised at how inaccurate the standard Rifleman's Rule is. I was surprised by how good of a job the Improved Rifleman's Rule did! Plenty accurate for most hunting situations! That said, it's not much more work to type a couple numbers into your cell phone's ballistic calculator.

Plots display the vertical difference for each method relative to the 'actual' ballistic solution as reported by JBM web calculator. Aka, how much you would miss by!
7mmRM was used for this calculation.

Standard Rifleman's Rule is good to 500 yards, or longer if the inclination angle is less than 10 degrees.
View attachment 215654


Improved Rifleman's Rule is surprisingly accurate for all but the largest inclination angles. FYI, this rule works better with a short zero distance.
View attachment 215656



And, if you apply no correction for shooting angle at all....
View attachment 215657
There are a couple common methods used, with varying accuracy.
  • Rifleman's Rule. Seems more common, but it not very accurate. Shooter gets MOA values from their 0-inclination range card for the horizontal distance range.
  • Improved Rifleman's Rule. What Dog Rocket explained. This method is surprisingly accurate, and imo is easier to do. Shooter multiplies the drop MOA values from their 0-inclination range card by the cosine(shooting angle).
-For both cases, use the wind values for the line-of-sight range with no correction factor
-If you want to convert your hold MOA to inches of drop, you have to use the horizontal distance to do so.

I went through this whole analysis last week as I became curious after some discussion in another thread. I was not surprised at how inaccurate the standard Rifleman's Rule is. I was surprised by how good of a job the Improved Rifleman's Rule did! Plenty accurate for most hunting situations! That said, it's not much more work to type a couple numbers into your cell phone's ballistic calculator.

Plots display the vertical difference for each method relative to the 'actual' ballistic solution as reported by JBM web calculator. Aka, how much you would miss by!
7mmRM was used for this calculation.

Standard Rifleman's Rule is good to 500 yards, or longer if the inclination angle is less than 10 degrees.
View attachment 215654


Improved Rifleman's Rule is surprisingly accurate for all but the largest inclination angles. FYI, this rule works better with a short zero distance.
View attachment 215656



And, if you apply no correction for shooting angle at all....
View attachment 215657
Dear speed,
Thanks for the perfect response. It is exactly what I hoped for.
Jim
 

73driver

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Joined
Aug 24, 2011
Messages
277
ACTUALLY ITS AN ART. If you would be in the bush without power for an extended period of time, all you gadget guys would be fu*cked. So in my opinion its rude to ask the guy what is he doing here. Maybe be nice and you can learn something. I've met a couple of great army snipers at the range in Bute, MT. They had no gadets, no computers, and reading the wind you can't even imagine. So, when you can do that, you can comment.
While on an extended back pack hunt you actually do not need but one LRF (laser range finder) with a tinny little spare battery. Right before you depart base camp for the back country just make up a drop card using your Ballistic APP with the temp, pressure and humidity you expect you will face during shooting hours for the next several days. This should be good enough for for shots out to 600 yards. I can figure wind more or less. But figuring out 250y vs 300y vs 350y etc out to 600/700y, well my eyeball just not calibrated as well as some claim. I did have a Leupold FX3 6X42 with duplex reticle and I had it all doped out to where I could figure if an elk or mule deer was at 300 yards or closer and knew my hold overs. Now a simple LRF that corrects for angle is as essential as a rifle that shoots sub MOA and a good pair of binos. With 400to450 yards being a near slam dunk shot (of course given wind and a shooter with decent skill) a LRF is a must, I just know I am not able to guess range past 200y within +/- 10 yards. Yep old school is cool but it has limits.
 
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BrentM

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I have read and am carefully considering all of the above. I have killed 40 elk, 10 of them with a bow. Only 3 of those were beyond 300 yards and they were one shot kills. With your help, I will keep it that way. Thanks to all.
Jim
You'll be in good shape. Steep slope angle shooting isn't just an issue with slope degree and distance it can and does change the rifle angle to the shooter. Just be aware of that and think about your positional shooting comfort for the angled shots. Apply the improved rule relative to MOA (assuming you shoot MOA) and not to distance and you'll be accurate. PM if you want some data.
 

Huntz

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NE Wisconsin
Holding low up or down hill has always worked for me.I have shot High Power for close to 30 years with an AR-15 out to 600 yards with a peep site.We had a spotter who would give you windage and elevation,but it was all done in the head.Every shooter also alternated as a spotter.Learning to read mirage is what give you X ring hits.You can over think shooting,but if you are hunting sometimes you do not have time to play with a Smart phone.I like gadgets,but only carry a rangefinder and have a cheat sheet with windage and range hold offs taped on my stock.Still before that kind of tech was available I shot my fair share of Elk,Deer and Speed Goats by simply stalking a s close as possible.That is how a real hunter eliminates errors and wounding animals.I like to shoot long range at gongs,but you can`t wound a gong.JMHO,Huntz
 

Warbird2006

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Apr 15, 2012
Messages
331
This is not accurate or true. Snipers use the latest gadgets and they do train in case of gadget failure but lives are the line. Shooting a range isn't a place where gadgets are overly needed or desired. A data book or even data in your head is enough to bang steel from a bench. There is very little people have in common with snipers so let's move past the bs or comparing a general long range hunter/shooter from a military sniper TEAM.

Since the beginning of long range data recording has been the norm. Data books recording all the intel you needed to place shots within relatively decent accuracy. It was developed using a fairly narrow base of cartridges and shared the same spec rifle to rifle. Today your data is at your finger tips and extremely accurate IF you know how to use it. You can pull a 223 to a 338 out of the truck and dial in shots with excellent accuracy. Enter the field environment of unknown situations, ranges, wind flow, barometric pressure changes, slopes, and unknow target sizes you have a need for accurate data. Top shooters all over the world use gadgets to get data. Temp, wind speed, barometric pressure or DA, drop data. Does that mean they'd be "f*cked" if their gadgets failed....no it does not. It means they use the best tech they can to make accurate shots first. Second, if they needed to use drop charts etc or dope book, they can. You'd be surprised how many people on this site can get by just fine in the event of electronic gadget failure. Don't assume they are not trained, practiced, or capable just because they prefer the most advanced tech available.
Actually, if you read what you wrote, you are proving my point. And I can not disagree with you. When you are on the range and ask any of the old shooters for a drop, bang bang. The young guys pull out their gadgets and are lost without them.
 

73driver

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OMG, doesn't anyone know how to shoot anymore without all this rule, adjustable scope, range finder, wind speed indicator & computer crap????????
Easy there cowboy. I get what you are saying, when I started hunting in 1970 it was with a SPFD receiver from between the wars, a barrel stamped spfd 9-44 a a lyman 4X scope older than I was. The second buck I shot was running at 250y and about 12deg down. It all happened fast and I took that buck right through the middle of the ribs. The next wildest shot was spooking a buck at 50y and swinging on it like shooting quail, I recall squeezing the shot off right before he disappeared behind the next clump of brush. That bullet blew off the top of his heart. My longest shot (now hunting with a new MOD 70 Classic 30-06 with fixed 6X leupold) was 370y on an elk using nothing but a Leupold duplex reticle to range with and memorized hold overs. Now I have refined my skills so that I glass up deer feeding or beded down, not many jump shots or shots on running game for this old curmudgeon. A Ballistic App on my phone is used to make up a drop card and hold over dope for my duplex Swaro on one 270 and my Zeiss BDC reticle on my other 270. Only "gadget" in the field is my range finder and it sure is handy to judge ranges usually between 250-350 yards. Yes I feel a little techno shooting bucks I glassed up in their beds but it is way more precise than my shots I wagged my holds on shooting at spooked game.
 
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Black Tail Hunter

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Oh, so you mean the use of gadgets is because of lack of training, that's a new one. But thanks for an honest answer.
In my case? Yes. My comments are anecdotal, as I have only my own experience to draw from. My shooting is 100% self taught. Can I determine the difference between 800 and 1000 yards without my rangefinder? No. Could I learn to range with my reticle? If I wanted to, but I prefer to use my gadgets, in the case they go down, I will grab my brush gun and stalk the timber. Again its preference not necessity.
 

BrentM

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Actually, if you read what you wrote, you are proving my point. And I can not disagree with you. When you are on the range and ask any of the old shooters for a drop, bang bang. The young guys pull out their gadgets and are lost without them.
I was too in the beginning. I was involved in counter sniper training in the military and was part of multiple exercises to try and not be a statistic. I was intrigued by the long range game and wound up getting private instruction from an army sniper and the quest to learn was set. Since then I have worked with several instructors and train long range courses as well. The world of long range is popular and developing and people desire to be part of it. Scopes, rifles, gadgets is all appealing to people. Their lives don't depend on the rifle nor the gadgets so often people could care less if they trained well enough to make a 800 yard shot on a game animal in ****** conditions. If their gadgets fail they will move into to point blank range or they will not a fill a tag that day. In the end, that is fine. I often find people start off simple and then dig into the details as they gain experience. Why did my data work yesterday and not today..... those are the guys who eventually need very little wizardry but still may prefer to use it. Heck I carry a LRF bow hunting and I have a range estimator in my sights in case of failure, but I practice range estimation all year anyway. I like tech but I don't want to rely it solely. Those new guys at the range will get there too.
 

BrentM

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I have found that tech, as I use it, is quite useful as a learning tool. If you feel a measured 10 mph wind enough times, you can get to know what 10mph feels like.
Exactly. Everyone starts somewhere.

I have a kestrel I rarely use but I have it with me. I haven't used an app or other tech device for wind solutions in years. At some point you do this stuff long enough that you just know. I use a short cut for wind. For example: .2 MOA per hundred per 5 MPH of wind. So a 5 mph wind is .2 and 500 yards its .2x500 or 1 moa. 10 mph would .4. If you half value wind or drop to 7 mph then it is .3 per hundred. So 500 yrds at 7 mph is 1.5. This data can easily be derived from an app and applied to the field and then just becomes of your memory bank.
 
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I know of a great park where elk appear before dark. Like many such places the convexity of the open area makes it unlikely to see elk when on the ground there. I found a cliff vantage point that would offer shots from 250 to about 600 yards. The downslope is 21 to 26 degrees. For me, the easiest method is to just apply the cosign rule. My question is whether you have found it reliable enough for steep shots at fairly long ranges. It is surprisingly hard to find a place to test this out.
 
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The cosine formula is tremendously accurate providing the angle & distance is carefully measured. I also hunt a lot of steep country that often presents steep downhill shots. I have tested my range finder that has the true horizontal distance calculation (tbr) in the display, an older Leupold RX-1200TBR. Lots of good tbr rangefinders on the market. My rangefinder is very accurate on distance both on flat ground & uphill / downhill. I was fortunate enough to be able to place targets at 50yd intervals out to 450yds on a 50degree slope. Impacts on target we’re virtually identical to flat ground. Since you have to use a rangefinder anyway you can forget about errors in calculating & using a table. Just range and shoot. I hope a big Bull is in your future.
 

Mustang72

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Can't we all just get along!!!
Yet another shooters request for learning getting derailed.
Use what works for you and continue to try and improve your skills and knowledge or be content.with where you are.
I guess I play both sides! I am more of an old school learn how to shoot through practice guy but if gadgets and apps help me then why not! Nothing wrong with either way As long as you know your abilities and limitations and respect the game you are hunting.
Even though I think it myself sometimes(can't anybody shoot without gadgets anymore) I see no point in hindering someday else's quest to learn. As somebody else stated -we all gotta start somewhere! Who am I to tell someone else how to learn!
 

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