Advanced Marksmanship How to convert inche drop at 1000 Yards to Mils
- Thread starter GBMaryland
- Start date
The "real math" isn't hard but its cumbersome to spit out in one sentence.
Quick 2-step overview:
step 1 trig for any 3 sides of a triangle = 3 known sides
step 2 more trig to get three angles (from 3 known sides)
More specifically, step 2 unfolds as follows ...
2.1 Trig function (cosine) using ratios of sides (soh-cah-toa) from 1.
2.2 Inverse-trig function (arc-cosine) to get angles in radians from 2.1.
2.3 Mil-radians conversion from 2.2
Quick 2-step overview:
step 1 trig for any 3 sides of a triangle = 3 known sides
step 2 more trig to get three angles (from 3 known sides)
More specifically, step 2 unfolds as follows ...
2.1 Trig function (cosine) using ratios of sides (soh-cah-toa) from 1.
2.2 Inverse-trig function (arc-cosine) to get angles in radians from 2.1.
2.3 Mil-radians conversion from 2.2
For some reason it's always been easier to remember by splitting it up into two thought processes for me...
I always remember the 1.047 and 3.6 numbers
Take which ever I'm using, and look at distance first.
Unit of measure x number of hundred yards gives me how many inches at that distance
3.6x10=36
Then take the inches and divide by that number
228/36=6.33333
For some reason that keeps it straight in my head and can be easier done off the cuff
Hope you've been doing well
I always remember the 1.047 and 3.6 numbers
Take which ever I'm using, and look at distance first.
Unit of measure x number of hundred yards gives me how many inches at that distance
3.6x10=36
Then take the inches and divide by that number
228/36=6.33333
For some reason that keeps it straight in my head and can be easier done off the cuff
Hope you've been doing well
Did you make the shot? I assume so since you were looking for MILs and didn't trust 22.8 MOA
. I hate how easy it is to convert inches to MOA but the cool kids use MIL so I guess I will
Wouldn't it be 21.8 moa ....Did you make the shot? I assume so since you were looking for MILs and didn't trust 22.8 MOA
It's a >10" difference being off a full minute, and enough to miss depending on the target
In my head I just use 1" per 100y but it's probably slightly more than that. If I was wrong, thanks you convinced me to never shoot MOA again because I couldn't get a simple 1000y conversion done in my head!!!
Yea "shooters" moa or inches per hundred is a common short hand.
About like using 3.5" instead of 3.6 for MIL conversion
Not trying to talk you our of anything, but if you are trying to convert numbers to true all your data then the 1 vs 1.047 or 3.6 vs 3.5 start to matter depending on how close you are trying to get your data
if you need operational 'redundancy', just carry spare battery/kestrel/iphone etc.
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.... can't decide if you think I'm trying to sell you on mils .... or trying to goat me into screwing with you about it .... hard to read inflection on the internet....
Anyway there is always error to be had in the rounding it's just how much everyone is comfortable with
I've chosen to shoot MILs even though MOA kinda makes more sense to me on the fly for estimation (but, as you pointed out even those estimates can be off by a bit at extended ranges). I went with MILs because it seems to be common among the guys I've learned from and I do like dialing in 0.1's instead of 0.25's.
All kidding aside, I really do appreciate you checking me on that because I've not run the number to see how much that rounding is off at 1k. And I'm just coping with having all MIL optics when MOA makes more sense to me intuitively haha
Yea about the same for me
Everything started in smoa
I was familiar with inches so it was easier
Now I just use the reticle and don't care as much
Now the .1 mil per mph wind bracket and dope plus a tenth per ten yards are like standard short cuts in my head... so everything is mils now...
I just memorized 1.047 / 3.6 and 3.438 / 3.44 if I need to convert for some reason all those are small enough numbers I can pencil it if need be
And I understand being confused...
Hell I now have 1/4 mil reticles ...
Dafuq
A simple rule that can help...
One mil is exactly 1/1000 of the distance to the target.
If you are shooting at 1000 yards, then 1 mil = 1 yard
If you are shooting at 1000 meters, then 1 mil = 1 meter
If you are shooting at a distance of 100 yards, then 1 mil = 1/1000 of 100 yards aka 1/10 of a yard aka 3.6 inches.
One mil is exactly 1/1000 of the distance to the target.
If you are shooting at 1000 yards, then 1 mil = 1 yard
If you are shooting at 1000 meters, then 1 mil = 1 meter
If you are shooting at a distance of 100 yards, then 1 mil = 1/1000 of 100 yards aka 1/10 of a yard aka 3.6 inches.
Get a databook as a backup. Have dope cards. People were doing this long before any of these electrical devices ever existed.EMP?
I, too, was an MOA diehard for the longest time.
Then I took a precision rifle course from Frank and Marc last summer and the light went on.
So for long range precision anything over 500 yds or so, I shoot MIL, for short range, general purpose shooting, MOA works just fine.
Remember, if you are using MOA @ 1"/100 yds vs 1.047"/100 yds, at 1000 yds and a 20MOA drop, you will be off by 9.4".
Just something to consider.
And don't even get me started about doping for wind.
Based off your bullet BC, which determines your "gun number", .1 mil/100 yds per wind mph is so much easier and intuitive.
For example, with a bullet BC of 650, that gives you a "gun number" of 6. So at a 6mph wind, you have a .1 mil offset every 100 yds. For a 12 mph wind, you have a .2mil offset for every 100 yds.
There is more to it than that, but basically, that's wind calling based on "gun number" and mils.
And don't forget ranging.
Using "gravity ballistics" you can dope your rifle out to 1000yds easily using mils.
Sorry for the long post.
Frank and Marc made a very strong impression on me in that course and I am a much better shooter because of it.
Then I took a precision rifle course from Frank and Marc last summer and the light went on.
So for long range precision anything over 500 yds or so, I shoot MIL, for short range, general purpose shooting, MOA works just fine.
Remember, if you are using MOA @ 1"/100 yds vs 1.047"/100 yds, at 1000 yds and a 20MOA drop, you will be off by 9.4".
Just something to consider.
And don't even get me started about doping for wind.
Based off your bullet BC, which determines your "gun number", .1 mil/100 yds per wind mph is so much easier and intuitive.
For example, with a bullet BC of 650, that gives you a "gun number" of 6. So at a 6mph wind, you have a .1 mil offset every 100 yds. For a 12 mph wind, you have a .2mil offset for every 100 yds.
There is more to it than that, but basically, that's wind calling based on "gun number" and mils.
And don't forget ranging.
Using "gravity ballistics" you can dope your rifle out to 1000yds easily using mils.
Sorry for the long post.
Frank and Marc made a very strong impression on me in that course and I am a much better shooter because of it.
Post #2 and #3 have the answer as generally known.
But for fun, here is this.
θ=s/r
where θ is the angle in radians, s is the intercepted arc, and r is the radius of the circle.
s=228”
r=1000yds=36,000”
So
θ=228/36,000
θ=0.00633333333….. radians
Multiply by 1,000 to convert to milliradians
6.3 milliradians
At 1,000 yards the use of 1" versus 1.047" per MOA is a large difference.
Why do you convert inches to anything? That's idiot math.Did you make the shot? I assume so since you were looking for MILs and didn't trust 22.8 MOA
Use angular measurements. Mils or moa it doesn't matter.
That’s a trap I fell into as I first started getting into long range shooting. Having been a carpenter for a few years I understand inches without any extra thought, but @Makinchips208 politely and kindly told me to forget inches as they don’t matter in this world and it sure simplified it for me. Why include extra math when we have plenty of it already?
Yea the ironic way I remember it myself is that not using MOA is worth more than a MOA at a half mile
This isn’t directed to the OP or anyone in particular but it amazes me how someone will dump a ton of money into a hobby or activity and just ignore learning the basics of how to properly use the gear they buy. Not to knock those learning or just starting out as we all gotta start somewhere but those who make the conscious decision to simply not learn or that just half ass it. I mean it’s your money and all but damn!
That’s a great explanation, thanks for that. I’m new to rifle shooting but this is definitely an easy thing to remember.
It's also useless beyond understanding the theory.
Learn how to use angular measurements only in the field.
For me learning those things helped me better wrap my head around mils. Granted, like you say it’s practically useless for the most part and I only ever use mil relation to linear measurements if milling a target, but it helped me gain a better understanding of what I was doing. If that makes sense.
It does make sense and it's important to understand the theory.
I was just cautioning the new guy that the field is no place to be doing all that cyphering.
I can’t disagree. I keep notes on me since I’m not going to remember formulas for using size of target and mil/moa on a scope to determine distance and mil/moa adjustments for specified range.
Granted, for when I’m “in the field” just means at the firing line of the range. I don’t hunt (severe lack of patience), not good enough for competitions, and any military field days are way behind me.
Learning a mil was 1 inch at 1000 inches and that a 1000 inches was 27.77 yards or 25.4 meters gave me an instant understanding of how the mil relation formula worked and after that I didn’t have to worry with keeping it memorized any longer. It was like a light switch being turned on for me. I absolutely suck when it comes to numbers and formulas, but understanding that relation just burned it into my mind.
I try to remember that when adjusting my scope that one mil at 100 yards is about 3.5” (3.6). And add 3.5 for every 100 yards after. I haven’t shot past 500 yards yet so I’m keeping it simple for now.
What helped me when switching from MOA to mil adjustment was thinking of each click as about 1/3rd MOA adjustments. That initially helped keep me from getting lost. 3 clicks is extremely close to 1 MOA.
Please explain how to do the math "properly".
1moa at 100 yds =1 inch/100 yds
1moa at 1000 yds = 1 inch*10 = 10 inches
1moa at 100 yds =1.047 inches/100 yds
1moa at 1000yds =1.047*10 = 10.47 inches
10 inches vs 10.47 inches = .47 inches (basically 1/2 inch)
So, say you are talking about a 20moa drop at 1000 yds,
Using 1 inch you get a 200 inch drop, when in reality, your 20moa drop would be 209.4 inchs.
Your impact would be off (low) by 9.4 inches, very large to be sure
but the basic difference is still only .47 inches/moa.
When talking long range shooting, precision is essential.
Anyway, maybe I'm reading your response wrong and if I am, my apologies.
OK...Let's look at an example
Suppose you're shooting a 308 175-grain SMK at 1,000 yards. The muzzle velocity is about 2,650 fps.
Per JBM or any other calculator, the bullet will drop 403.2 inches at 1,000 yards. How many MOA is that?
Using 10" (1" per hundred yards) gives us 40.32 MOA of correction.
Using 10.47" (1.047" per hundred yards) gives us 38.51 MOA of correction
The difference is 1.81 MOA, which is 18.95" @1,000 yards.
You'd miss a 20" plate completely.
And really if you’re going about it that route you should be working out your drops off range before you ever leave the house. How hard is it to just simply do the actual math at that point?
If you’re waiting to get to the range and then looking at inch drops and trying to convert on the fly you’re doing it wrong.
You're correct in that regard, but the point of the example is not how to do it in the field but why not to use 1" versus 1.047.
When in the field, use your calculator or DOPE tables. Your calculator doesn't make those errors, and your backup DOPE table shouldn't either, or they are worth nothing.
Precision shooting is precision in all aspects.
That’s a little eye opening and could be one reason why I’m missing an 8” or 10” plate at 500 yards. Thanks for a great explanation!
WHY?
Make a drop and windage chart in milliradians or true minutes of angle (whichever unit your scope adjusts in).
Dial in the correct drop in mils or moa for the distance to target. Do the same for windage.
Place the center of the reticle in the center of the target and fire.
There is ZERO need to convert from inches to milliradians or to moa. NONE. Stop making this more complicated than it needs to be.
If keeping it simple is your goal, your current approach is counterproductive.
Aside from any marksmanship or wind estimation errors, you're missing because you're introducing errors from completely unnecessary arithmetic.
Because my targets are in inches. So if I shoot 2 inches low at 100 yards then I know I can dial up 6 clicks or .6mils. I don’t have a chart for my ammo for each range because I’m still practicing basic marksmanship skills and using whatever cheap ammo I can find.
I suppose I can print targets in cm’s and then forget the conversion. But since the range near me has target placement at yards, my targets are inches, and I have another rifle with an moa scope (soon to change to mils), I guess it makes sense to me to read the target in the inches that it’s in and remember the rough conversion to mil adjustments.
