# How close is the cosign rule in slope shooting?

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#### epags

##### Well-Known Member
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
Please, can you tell me where I can find these graphs to down load.

#### redleg1013

##### Well-Known Member
It depends. If the slope is a straight line between two points then cos will hold up. If the slope is concave then the angle is an average, then you'll have to figure cos against an average rate of change [f(b)-f(a)]/(b-a) to be close, or go through the whole cosine of the instantaneous rate of change maths if you want to be precise.

#### skipdavidson

##### Well-Known Member
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
Perfect demonstration of the ineffectiveness of the Riflemans rule. It works out to 500 and 20 deg, but note that if you do nothing, that also works out to 500 and 20 degrees! Nice job, thanks for taking the time to present this data. So much more effective demonstration than the story style "this one time in elk camp..."

#### speedengineer

##### Well-Known Member
Please, can you tell me where I can find these graphs to down load.
I made them. Fairly straightforward to do for your rifle if you're curious. I used Excel, but google sheets would work too.
1. Generate your ballistic trajectory for horizontal fire using your favorite ballistic calculator. I used JBM web calculator
2. Calculate your RR or IRR correction for each range just like you would do in the field
3. Generate more 'true' ballistic trajectories for various shooting angles that you want to compare to
4. Plot the difference in drop using the plotting tools in excel/google sheets.

#### TxHeartShot

##### Active Member
OMG, doesn't anyone know how to shoot anymore without all this rule, adjustable scope, range finder, wind speed indicator & computer crap????????
Easy dude...even Daniel Boone had trouble with inclines! Back in the day I suppose "a hopeful guess" was the method, which probably too many times resulted in a cold miss or a wounded animal. The smart kids use what technology they have to avoid those negative outcomes.

#### brcfo_outdoors

##### Well-Known Member
I think as hunters, conservationists, and sportsmen we have an obligation to be ethical and humane. Because we are challenging ourselves to kill at longer ranges than the average hunter, we have a moral obligation to do so with the greatest precision possible. That means employing the best techniques and tools available to us, whether they be an actual in-field ballistic calculator, or a validated dope card in addition to practice and repetition. Knowing your own capabilities and limits is far more important than your prejudice for someone else's.

#### Tikkashooter

##### Well-Known Member
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.
If a guy is shooting at a known range on flat ground you wouldn't use a rangefinder or any "gadgets" anyway.Wind reading "gadgets" don't usually work very well being wind is so variable between you and the target. You seem like you don't have a whole lot of knowledge on the topic other than watching some guys make some wind calls on a range

#### docmark

##### Active Member
Am I missing something? The OP said up to 600 yards and if I read the graphs correctly the "Rifleman's Rule" is off by ~3'' at 600 yards and the "improved Rifleman's Rule" is off by ~5". That would make the improved version LESS accurate at 600 yards

#### fishingstockwell

##### Active Member
This has been a great thread for me to digest. I’m continuing to progress in my long range shooting. My rifle is more than capable, consistently shooting in the .3-.5s. In the past I have used the corrected horizontal value given by the Leica 1600. From what I have read in this thread, I’ve been using the Rifleman’s solution.

a quick studied on determining cosine appears to be that you would divided the corrected horizontal value by the line of site value to get your cosine. Once you have quickly determine your cosine with some very basic math, you would then multiply the cosine value by your dope for the line of site value to get the improved rifleman’s solution.

it appears that a basic drop chart taped to the gun and this formula would be adequate for most shooting solutions in hunting conditions out to roughly 800 yards, and certainly better than just using the corrected horizontal value give by the rangefinder with TBR capability.

Please correct me, if I have missed something, or have my formula wrong. Again, great thread and yet another advancement for the development of my long range hunting abilities. Great site and great knowledgeable members willing to help those still climbing the learning curve.

Thank you,
Matt.

#### Dog Rocket

##### Well-Known Member
Am I missing something? The OP said up to 600 yards and if I read the graphs correctly the "Rifleman's Rule" is off by ~3'' at 600 yards and the "improved Rifleman's Rule" is off by ~5". That would make the improved version LESS accurate at 600 yards
I don't know what data was used to generate those charts, but here it is from JBM:

308 w/175 SMK @ 2630 fps @ 2000 ft elevation:
600 yard flat drop in inches = 15.1 MOA = -95" drop

600 yards, -30* slope RR = 519 yards = -64.5" drop

600 yards, -30* slope IRR = 13 MOA = -81.6" drop

600 yards, -30* slope actual = 12.5 MOA = -78.5" drop

#### Rich Coyle

##### Well-Known Member
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.
You are not making sense. Very few of us are pro athletes but certainly know enough to comment on them. Same here. Your snipers are extremely rare. And yet some here using their tools can match them.

#### Dog Rocket

##### Well-Known Member
I don't know what data was used to generate those charts, but here it is from JBM:

308 w/175 SMK @ 2630 fps @ 2000 ft elevation:
600 yard flat drop in inches = 15.1 MOA = -95" drop

600 yards, -30* slope RR = 519 yards = -64.5" drop

600 yards, -30* slope IRR = 13 MOA = -81.6" drop

600 yards, -30* slope actual = 12.5 MOA = -78.5" drop
7mm Magnum with a high BC bullet @ 3,000 fps is similar.

600 yards flat: 10.2 MOA = 64.1"
RR = 519 yards @ -30* = 7.9 moa = 48.2" drop
IRR = 8.8 MOA = 55.2"
Actual = 8.4 MOA = 52.6"

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#### TexasSportsman

##### Well-Known Member
One of my college friends disagreed with the advancements in hunting equipment and said it wasn't a fair hunt. I told him hunting isn't supposed to be fair. I asked him if he knew of the native American practice of chasing buffalo over a cliff. The women and children waiting below quickly made use of the tools they had to field dress multiple kills.

I also shared with him that wolves hunt in packs and aim for the weak, the young and the old by separating them from the herd then taking them down. Its a very efficient way to hunt.

The wolves hunt there way and we hunt ours. If hunting were supposed to be fair our species wouldn't have made this this far. We have to use our superior intellect to our advantage whether in business and out in the field or river to bring back food for the table.

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