Mil Dots and Elevation Holds

12581 Views 14 Replies 7 Participants Last post by m141a, Mar 28, 2010

USMC 0311

Discussion Starter · Mar 27, 2010

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

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USMC 0311

Discussion Starter · #7 · Mar 27, 2010

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

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USMC 0311

Discussion Starter · #8 · Mar 27, 2010

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

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USMC 0311

Discussion Starter · #11 · Mar 27, 2010

unclenick said:
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

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