Holdover With .308 @ 300 Yards?

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deadeye1122

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I have a nikon monarch 4/16/42 nikoplex on a rem 700 .308. Have not shot yet to much snow. Nikon states that the distance between the duplex post (for lack of a better description) top to bottom is 16 inches sighted at 100 yrds @ 4 power. So if your Federal power shock 150 gr drops 17 inch @ 300 yrds would you hold over twice the distance from the cross hairs to top of the bottom post? Thanks and forgive me for my lack of termonalagy. Deadeye
 
deadeye,

I changed your thread title to try and make it clearer what you were asking about. I hope it helps, if you don't like it PM me and I'll change it back.

What zero are you using to have to worry about being 17 inches low at 300 yards? Looking at the tables at http://www.federalpremium.com/products/details/rifle.aspx?id=33 , you must be using a 100 yard zero, I'd guess. A certain number of folks hunting deer etc. under usual circumstances will zero a .308 at about 2.5" high at 100 yards, that gives you about 3" high at 200, puts it dead on at about 250- 275 and makes it necessary only to hold a little high (3- 4" or so) on the animal at 300. And it gives more room for error in range estimation within the range at which most shots are taken. Of course it's necessary to check what a given rifle and load will do at various ranges on paper before trusting it in the field... and for shooting at genuine holdover range (by that I mean holding over the animal completely) the shooter needs to practice enough at long range to be sure of their zero and ability to estimate range and wind drift to get clean hits. If in doubt- don't shoot, where an animal is concerned.

hth,

lpl
 
I agree with Lee. 17" sounds like A LOT of drop from even a 100-yd zero. Zero your .308 at 200 and you only have to worry about 7-8" of drop to 300, half of what you are describing.
 
I have a 230 yd zero on my .308, which gives me 6" of drop at 300 yards. I just hold at the top of a 12x12 target at that range, puts them right in the bullseye.:)
 
the ballistics for the 155 AMax that i use for target shooting say that with a 100 yard zero, bullet drop is 13.38 inches with standard atmospheric conditions.

that aside, if you're shooting at 300 yards, you need to know what the distance is between the cross and the top of the post is at 16x at 100 yards, then divide it by three and use that to figure holdover for 300 yards. using 4x at 300 yards isn't going to do you much good and defeats the purpose of having a 16x scope.
 
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Thx for the replys. Thx Lee for changing the title. Was trying to see if I could use the scope as a rangefinder. I used 100 yrds @ 4x as a starting point as per nikon charts. will most likley use a higher magnafacion.Bobarino is on track with what I was asking. Thanks again.
 
Your Reticle sustention value(RSV) of 16" at 100y on 4X, will equate to 48"(RSV) at 300y on 4X, so imagine your reticle opening(as you say, between the posts) divided into 10 equal units....

Long problem short...you would need to hold over 3 of those 1/10th units(3/10th's) to come-up 16" at 300y. APPROXIMATELY

48"(RSV) / 10 units = 4.8" per unit value at 300y on 4X~
16" of drop / 4.8" per unit value = 3.3 Units~
4.8" per unit value X 3.3 units = 15.84"(close enough to 16" huh?) of come-up needed~
 
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I believe the reticle should be on the 2nd focal plane with that optic. If so, it is possible they have a simple range estimation feature built into their reticle such as the Leupold Vari-X III on my 7mm. Leupold placed the numbers 2 to 6 along the power adjustment ring with the '2' at the 4.5x and the '6' at the 14x magnification. The reticle is designed such as yours where the distance from the tip of the bottom post to the intersection of the crosshair is 16" at 200 yards on 4.5x. Because the reticle is on the 2nd focal plane, its dimensions change with magnification. This was intentionally designed to help estimating range. A deer is typically said to be about 16 inches from backbone to brisket. So by simply adjusting the zoom level on my Leupold until his chest is bracketed in the crosshair, I can get a rough range estimation by checking the indicated number next to the zoom level. Personally, I know if I am up above the 8x or so where the '4' for "400 yards" is, my abilities are going to be stretched and I should pass.

You should make some targets that are 16 inches tall, and find yourself a range that allows you to walk them out 500 yards or so. Experiment with the magnification range and see if a similar system is built into yours. I am guessing it is.
 
Let me make sure I understand this properly (I've only got one scope one one rifle, so I'm not extremely well versed in all the math on optics).

Are you talking about range estimation based on crosshair distance at "X" power?

OR

Are you talking about a point of impact change based on "X" power?

I hope I've worded that properly.
 
Gunnutery, In mp OP we know the distance a 100 yards between the posts ( sustension Thanks Unckle Mike for teaching me the terms) is 16 inches. A federal 150 grain drops aprox 15 inches at 300 yards. I was trying to make a regular scope cross hairs in to a BDC type scope. Uncle Mikes post seems to right on but will have to think on it some. As I said I have not been to the yet and that is the only sure way to kmow. Thanks for all that responded Deadeye
 
In the target games, we call it 5 moa sight change from 100 to 300 yards.
'Bout a mil and a half if you use that system.
I don't know the reticle you describe, but you should be able to cipher it out.
 
Deadeye...if dividing your reticle into 10 equal units is too busy for you....you can imagine your reticle divided into 5 equal units. As follows....

48" (RSV) / 5 units = 9.6" per unit value at 300y on 4X~
16" of drop / 9.6" per unit value = 1.7 units.... so you would hold 1 3/4 (1.7) of your imaginary equal units over the POI you desire.

to check it....

9.6" per unit value X 1.7 units = 16.32" (Close enough to 16" for government work!) lol
 
UM's got the system down!

It's all based on the mil-ranging formula (for both downrange zeroing and rangefinding) and the ~inversley proportional nature of 2nd FP reticles--the 1 u have Deadeye.

That optic also subtends 4.3 inch per hundred yds. (IPHY) at 16x. So from x-hair to plex post tip (PPT) is 2.15 inch per 100 yds. So if u're 6" low at 300 yds. then here's the equation--

6 x 100 / 2.15 / x = 300

x=0.9, so aim 9 tenths the distance between x and lower post tip @300 yds. and u'll hit what u're aiming at.

Rangefinding is the same formula above, only now the "6" figure becomes the tgt. size variable.
 
Whatever you gain from all this type. Do shoot your rifle at the various ranges that you might encounter. No amount of internet calculus will put your mind at ease as much as putting holes in paper and seeing for yourself what happens.
It's pretty simple really, and I can't even read some of these posts.
 
Then you have the scope adjustment value....It's called the 'Turret Adjustment Value' (TAV) The amount of clicks to 'Dial On' the scope.

Instead of using Kentucky Windage, or Hold Over as seen through the scope.....

Your Nikon has a Turret Adjustment Value of 1/4" at 100y~

The TAV for your scope at 300y will be 3/4" (.750"), each 'click' of the turret you make will move the POI three quarters of an inch at three hundred yards.~

Your drop is 16" at 300y~

So it's....
Bullet drop at Range / TAV of your scope at range = Number of clicks to adjust turret.

16"(bullet drop at 300y) / .750"(TAV for your scope at 300y) = 21.3 clicks need to be able to aim dead on at 300y.

Check it.... 21 (clicks) X .750" (TAV for your scope at 300y) = 15.750" (15 3/4") close enough!

Find your scopes TAV(at the range your wanting to shoot) by taking the scopes adjustment value at 100y and multiplying it by the range to the target....ie... TAV at 300y is.... .250"(your scopes TAV at 100y) X 3(300y) = .750"

all fun....you see, math ain't all that bad....or is it?!?!

I might have done better in school if we had worked these kind of problems! lol hehehehe
 
Hey, as Blitzen says, the only 100% sure way to know exactly the various data for your rig at various atmospheric conditions and ranges is to get out there and do some shootin'.

But this math stuff is fun to do on those rainy days when you can't be shooting!
 
I wish I wouldn't fell asleep in calculus 101. There are very knowlagable people on this form and I appreciate their input. Some I can understand quickly and some goes right over the top. I haven't been to the range yet so blitzen's post is spot on. Shoot and see. Holes in paper will tell what will work for me. Thx again for all your input, Deadeye
 
In the time it took me to think out and type my 4 plus lines of reply to you, you guys wrote a chapter of scope basics 101. Your amazing!!
 
Some of us just shoot to much and drink to much, (but never at the same time) and like to spout off on the internet!! :)
 
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