Shooters Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
I dont have all the information probably needed but in a nut shell im looking at purchasing my first Mil Dot scope to go on a nice .308 i have been eyeballing for awhile. Im planing on putting some HPBT Sierra 175Gr. rounds with a Muzzle Vel. of 2600 FPS. with a G1 Ballistic Coefficient of 0.496 through this rifle. Im trying to figure out the Elevation holds if i was to zero this rifle at 300 Yards due to my limited range access. I have been racking my brain for the past 2 weeks trying to figure all this out and im to the point where im just exhausted and frustrated on not being able to figure this out on my own. According to what i have found in my Ballistics book the PATH IN INCHES IS AS FOLLOWS : 100 yrds +2.2 , 200 yrds 0.0 , 300 yrds -9.1 , 400 yrds -26.1 , 500 yrds -52.4 , 600yrds -89.5 , 800 yrds -204.8 , 1000yrds -393.0
WIND DRIFT IN INCHES AS FOLLOWS : 100yrds 0.7 , 200yrds 3.0 , 300yrds 7.0 , 400 yrds 12.9 , 500yrds 21.0 , 600yrds 31.3 , 800yrds 60.2 , 1000yrds 111.2

If anyone can compute this for me and repost , as well as explain how you did it i would be very thankfulfor your time on this irritating issue im having. My book has an example with a .308 Fed. 168Gr. with a (600yrd Zero) as follows

yards Inches Mils
900 +158 +5.0
800 +88 +3.0
700 +36 +1.5
600 Zero Zero
500 -23 -1.25
400 -35 -2.5
300 -37 -3.0
200 -30 -4.0
100 -18 -4.5

Since the above chart is set for a 168Gr. bullet and zeroed at 600yrds , im only going to ASSUME that the round i want to use 175Gr. is heavier and that i want to zero at 300yrds there for the chart above would be incorrect. SO im asking for help on trying to figure this out cause my brain is fried , as much as i want a mil dot scope im just frustrated and about to give up with the mil dot idea. You all are my last hope on trying to "BREAK THIS DOWN BARNEY STYLE" for me. Thanks again
 

·
Registered
Joined
·
816 Posts
As far as Mil-Dots go this is the basics. A Miliradian is equal to 3.6 minute of angle. Thus at 100 yards it is equal to approximately 3.6", at 200 about 7.2", 300 about 10.8" and so on. The reason I say approximately is that a minute of angle is not exactly 1" its actually just a hair over but don't worry about that right now.

If you are going to buy a mildot scope I will assume it will have some type of tactical or target turrets on it. In that case you will probably find it easier to just zero at 100 yards and then dial the elevation turret to the desired point for each shot at various yardages. For instance, if you are shooting the 168 grain bullet and are zeroed at 100 you would dial up 2 MOA to shoot 200, dial up 5 MOA for 300, 12 MOA for 500, you get the picture. You could also use the mildots on the scope to holdover the target but its more precise to dial up to the range you are shooting.

As far was wind drift goes the numbers you posted are for 10mph full value winds. You will have to read the wind and adjust accordingly. There is a simple formula you can use to get you in the ballpark which is: R x V / 15 = MOA adjustment or hold off. "R" is range in whole numbers such as "2' for 200 the "V" is wind velocity in mph and you divide by the constant of 15. Example: 3x10/15=2MOA. 2MOA at 300 yards would be 6" and as you can see from the chart you posted it is within an inch of the published data. This is where I like the mildots because I can just hold off for the wind and not adjust my turret for each shot since the winds can change quite a bit from shot to shot unlike the drops which are fairly constant unless there is a drastic change in temperature, humidity, slope angle, or altitude. I'm not sure if I gave you the info you wanted but I hope this helps.
 

·
Registered
Joined
·
816 Posts
I forgot about the bullet weight issue. I don't know how far you are planning on shooting but the 168 is fine out to 600 yards. If you want to shoot further than that I would go with the 175. Of course it would not be a bad idea to try them both as you may find your rifle shoots one better than the other.
 

·
Banned
Joined
·
2,380 Posts
i thank you for posting that info..it might be the seed ,,for my knowledge to grow in this regard. mabe..slim:)
might be simpler for me to just know the scope an rifle of my 2 favorite rifles..06 an 22.
heck even thats gets about to my limits ..i say this since ive got two favorite rnds for each gun .an holdover is of course different for just these ,,at variouse estimated ranges..slim
yall excuse me i just started my first cup ,this morning. i might start making sense ,oh lets say about bed time..grin.
a side note ..its funny to me how a cup o coffe gets me cranked in the morning an danged if it don t put me to sleep at night.. probably not your average bear ,though..[yogi bear] ,for those who think ive finally went round the bend..
 

·
Registered
Joined
·
639 Posts
Inches divided by range in hundreds of yards equals MOA. So with your first set of numbers 158 divided by 9 (for 900 yards) equals 17.6 minutes of angle. Divide that by 3.6 to get mils. 17.6/3.6=4.9 mils (rounded to 5).
 

·
Registered
Joined
·
639 Posts
Sniper Formulae

Here are some formulae that you may find useful in your long range shooting. But first, a few words concerning Minutes of Angle (MOA) and Mil (milliradian) dots.

Both MOA and mils are used to measure angles. There are 360 degrees in a complete circle. There are 60 minutes in a degree. A radian is defined as the plane angle with its vertex at the center of a circle that is subtended by an arc (not a line) equal in length to the radius. There are 2 times Pi (6.283...) radians in a complete circle. A milliradian is simply one one-thousandth of a radian. We take the mil to mean a distance equal to one one-thousandth of the distance to the target. The Army further confuses things by defining a milliradian as 1/6,400th of a circle. Army mil-dot reticles are very slightly different -from- the Marine Corps mil-dots.

As shooters we tend to think of one MOA as equaling one inch at 100 yards. Our scopes are usually calibrated to give us one-quarter (or one-eighth, or one-half, or one, unless it’s metric then you get about one-third) inch adjustment per click at one hundred yards. The scope manufacturers don’t say “quarter minute clicks” but that’s how we interpret it. A true MOA is equal to 1.047 (rounded off) inches at 100 yards. The difference is minor. Even at 1,000 yards it’s slightly less than a half an inch, but it is there. Where we get into trouble is when we start running numbers up on the calculator. One true milliradian equals 3.438 (rounded off) true MOA. This means one true milliradian equals a very tiny bit less than 3.6 inches at one hundred yards. 3.6 inches at one hundred yards or 36 inches at 1,000 yards is exactly how we want to use the mil. If you think your calculator is telling you that a mil equals 3.438 inches at 100 yards you are mistaken. Fortunately, the differences are too minor to make a difference.

Just remember that for shooting purposes, virtually all scopes, reticles, and shooter’s formulae are calibrated so that one MOA equals one inch at 100 yards and one mil equals one yard at 1,000 yards.

1 actual MOA = 1.047 inches at 100 yards
1 actual milliradian = 3.438 actual MOA
1 actual milliradian = 3.600 inches at 100 yards
1 actual MOA = .291 actual milliradians
1 Army mil = 3.375 actual MOA
1 Army mil = 3.534 inches at 100 yards

1 shooter’s MOA = 1 inch per 100 yards of range
1 shooter’s MOA = .278 mils
1 mil = 3.6 shooter’s MOA

MOA adjustment times the range in hundreds of yards (600 yards = 6) equals change of impact in inches.
MOA X R = Inches

Inches adjustment divided by the range in hundreds of yards equals MOA.
Inches/R = MOA

Desired MOA adjustment times the resolution of one click equals total adjustment in clicks.
5 MOA X 1/4 (.25) minute clicks = 20 clicks

I prefer to memorize my come-ups in clicks rather than MOA.
Total drop in clicks -from- a 100 yard zero minus the total clicks of all come-ups to the new zero range equals your come-up to that range. Start at 200 yards and work out.
Clicks at 500 yards minus come-ups to 200, 300, and 400 yards totaled equals come-up -from- 400 to 500 yards in clicks.

The height of an object in yards times 1,000 divided by the apparent height of the object in mils equals the range in yards. Height in meters yields range in meters.
(Height X 1000)/mils = Range

The apparent angle in degrees -from- vertical of mirage divided by 8 equals the windspeed in miles per hour. Mirage angle must be read with the wind blowing directly -from- the right or left. Turn your spotting scope if you have to.
Angle/8 = MPH

The apparent angle in degrees -from- vertical of smoke, flags, or the arm pointing at lightly balled piece of paper dropped -from- the shoulder divided by 4 equals the windspeed in miles per hour.
Angle/4 = MPH

The Marine Corps Windage formula:
Range in 100s of yards (600 yards = 6) times the wind in miles per hour divided by the constant C equals MOA change.
(Range X MPH)/C = MOA
For the M118 round at sea level
C = 15 for 100 to 500 yards
C = 14 for 600 yards
C = 13 for 700 to 800 yards
C = 12 for 900 yards
C = 11 for 1000 yards
For the M852 round at sea level
C = 13 for 100 to 200 yards
C = 12 for 300 to 400 yards
C = 11 for 500 to 600 yards
C = 10 for 700 to 900 yards
C = 9 for 1000 yards
 

·
Registered
Joined
·
8 Posts
Discussion Starter #7
In response to RangeJunkie

Very Very Helpful , just one thing , i understand the formula you provided for wind drifts , as far as X= 6In. at X Yards and so on , but once you figure out the Inches how do you know how many mils that is to ..... LEAD so to speak since MILS are in decimals or do i refer to my ballistics book that has the estimated windage for the predetermined windage movements but even in the book its in inches. Im sorry if this seems manotenance , the pieces ar falling into place so to speak just need to scrub my brain one last time hopefully. Thanks again for any and all info
 

·
Registered
Joined
·
8 Posts
Discussion Starter #8
In response to Sionaprhys

Im begininng to understand and comprehend the concept with everything now but still unsure with all these mathmatical equations being thrown out there from what i have read is this :

MARINE CORPS. WINDAGE FORMULA IS:
Range x MPH / C (Constant)

100-500yrds C=15MOA
600yrds C=14MOA
700yrds C=13MOA
900 yrds C=12MOA
1000yrds C=11MOA

But i have also read THIS : Inches to Mil :
EX. 158In. / NUMBER IN YRDS EX. 9 = 900
158/9 = 17.6 MOA DIVIDE 17.6 / 3.6 = 4.9 Mils

So ..... Would i convert the ABOVE MOA's using this method to get my windage adjustment or LEAD in Mils ???? Everything is coming together , just slowly since im new to this ( its making sense just with all these mathmatical equations being put out i dont know which one to follow to get my WINDAGE IN MILS
 

·
Registered
Joined
·
639 Posts
The windage formula is only a way to estimate your windage MOA. The best way is to use actual measured windage on a known distance range with your rifle. Next best is to work from a chart run on a computer program. However. . .

With standard M118 7.62 NATO at 600 yards with a 5 mile per hour full value wind you would use the following-

6 (600 yards) x 5 (5 miles per hour)/ 14 (C constant) = 2.1 minutes of angle.
6 x 5 / 14 = 2.1

2.1 MOA x .278 = .58 mils.
Or 2.1 MOA / 3.6 = .58 miils. Either way.

C is the constant multiplier and not your minutes of angle.

So at 600 yards with a 5 mph wind coming directly from the right or left, I would hold a half a mil into the wind.
 

·
Super Moderator
Joined
·
13,431 Posts
The 175's behavior is pretty close to the old 173 grain FMJ in M118, but not exactly. I'm sure the military has some pretty exact tables for the 175 gr. SMK from m24's, since they use it in M118LR.

Going back to the OP, if I simply run ballistic tables in QuickTARGET, I can define each click of sight correction as having 3.375 moa. The output in clicks then gives me the necessary hold-off correction in mil dots in the scope reticule (assuming the magnification is correct for the reticule's calibration).

A couple of points: I ran this both with Sierra's published G1 BC's and velocity break points and with the G7 BC (VLD standard projectile). Since the projectile is neither a G1 form nor a G7 form and falls inbetween, I averaged results of these two to try to get a better calculation. Be aware it will not be exact unless the drag function for the 175 gr. SMK is defined exactly in your barrel.

I also ran the tables with the wind coming from both the right (first chart) and the left (second chart) for wind correction per mile per hour. That means you take those numbers and multiply by the speed of the wind in mph that you actually have.

Note that the correction is not zero for a straight on zero degree wind. This is due to precession of the bullet.

For the tables below, the muzzle velocity is 2600 fps and the barrel has a 10" right hand twist. Precession will change with twist and will reverse direction for a left hand twist. The sight zero is 300 yards.


Wind from Right:




Wind from Left:

 

·
Registered
Joined
·
8 Posts
Discussion Starter #11
The 175's behavior is pretty close to the old 173 grain FMJ in M118, but not exactly. I'm sure the military has some pretty exact tables for the 175 gr. SMK from m24's, since they use it in M118LR.

Going back to the OP, if I simply run ballistic tables in QuickTARGET, I can define each click of sight correction as having 3.375 moa. The output in clicks then gives me the necessary hold-off correction in mil dots in the scope reticule (assuming the magnification is correct for the reticule's calibration).

A couple of points: I ran this both with Sierra's published G1 BC's and velocity break points and with the G7 BC (VLD standard projectile). Since the projectile is neither a G1 form nor a G7 form and falls inbetween, I averaged results of these two to try to get a better calculation. Be aware it will not be exact unless the drag function for the 175 gr. SMK is defined exactly in your barrel.

I also ran the tables with the wind coming from both the right (first chart) and the left (second chart) for wind correction per mile per hour. That means you take those numbers and multiply by the speed of the wind in mph that you actually have.

Note that the correction is not zero for a straight on zero degree wind. This is due to precession of the bullet.

For the tables below, the muzzle velocity is 2600 fps and the barrel has a 10" right hand twist. Precession will change with twist and will reverse direction for a left hand twist. The sight zero is 300 yards.


Wind from Right:




Wind from Left:
According to the charts you submitted to me makes sense but my only question is this ...... According to what you submitted (IN THE CHARTS) is dot adjustment PER MILE AN HOUR OF WIND

So in the chart one of the marks is -2 dots (PER MILE AND HOUR OF WIND) so if im reading your explination correctly : IF I HAVE A 15 MPH CROSSWIND , YOUR CHART SHOWS -2 DOTS SO TIMES THAT BY 15 WHICH WOULD GIVE ME (-30 DOTS) IS THAT CORRECT ?? IF SO HOW SO ??? ISNT THE MAX DOTS ON THE SCOPE 10 UP/DOWN , 10L/R ???? Keep in mind im new to this so this may seem like i dumb question but im merely asking
 

·
Super Moderator
Joined
·
13,431 Posts
No. That's way too much. I set the software on autopilot and it looks like the default wind speed of 10 mph instead of 1 mph kept reasserting itself. That'll teach me to do this stuff in a hurry. I'll fix the table.

Nope. That's not what happened. As soon as I started to redo them I recalled what actually happened: I set out to do dot/mph, then realized it gave a lot of leading zeros that were hard to read, so I decided to switch to dot/10 mph and forgot to change the labels. Any way, I'll fix the labels.

Also note that they are zeroed at 300 (whatever the wind) and the tables correct off of that for the same wind speed. I think that may cause confusion? I think I'll redo them with total wind deflection instead, thus assuming the 300 yard zero is established in zero wind. Then you can go left or right of that as compensation calculators usually work.
 

·
Super Moderator
Joined
·
13,431 Posts
OK. This turned out to be quite a little adventure, uncovering no less than two bugs in QuickTARGET V. 3.6 that QuickTARGET Unlimited V. 3.6 does not share. As a result, until there is a fix, if you own these programs, do not trust QuickTARGET for windage calculations on projectiles with multiple G1 BC's, but run those in QuickTARGET Unlimited instead. It is more work to set up, but the calculations are accurate. I'll e-mail the bug data to Hartmut. The last time I found one in QuickLOAD he fixed it immediately for the next issued version.

So, here is the correct information, still averaged for the G1 and G7 models. The G7 may actually be the more accurate of the two because it is based on Litz's actual measurements from real guns of the bullet's velocity losses over a range rather than relying on Sierra's published information as the G1 BC's do. However, I stayed with the averaging because of the fit issue previously experienced. There is a maximum difference of 6.7" elevation at 1000 yards. By averaging, even if you assume one of the two is correct and the other is wrong, then the error is cut in half.

Note that one of the bugs I found is that QuickTARGET produces wind correction (in moa only) oppositely signed from QuickTARGET Unlimited's result. QTU is correct as far as mil dots in a scope are concerned. That is, if the wind blows from the right, assuming you make no click corrections, you will have to hold the reticule to the right, putting the target on the line to the left of the cross hairs. If the cross hairs define the X and Y lines of a standard Cartesian coordinate plane with 0,0 where the hairs cross, then the portion of the line held over the target to correct for wind is on the -X side of the center. Also, if you have to hold over, the vertical line below the crossing point is on the target, that is the -Y side of the line.

I also went ahead and added a decimal place so the windage corrections are truly in dots per mph. It looks uglier, but I'll leave it to you to multiply.

Based on the bugs I found, I would just ignore the first charts. They aren't way off but are off.

 

·
Banned
Joined
·
3,948 Posts
I have shot scopes with the mil-dot recticules and there is a link on the internet for those that wish to learn all about using mil-dots. I'll try to post that later in the week. I have a Bushnell Tactical 5 x 15 power with ADJ AO on my .308 FAL.

It is a very accurate rifle that falls under .500 MOA off the bench. I personally like mil-dots verses the so calle varmint/predator scopes that Leupold and some others have on the market. I carry a laminated card on the side of my rifle for refference out to 700 yards. This is not a guided laser deal but it usually helps much better than just using a convential rifle scope.;)
 
1 - 15 of 15 Posts
Top