Advanced Marksmanship Drop charts

[clayne_b]

First of all great Forum.... I have a few questions about building drop charts, i have a chronograph, if i get a bc at 4700 feet and build a chart off that info with a program, but my hunt is at at 10-11000 feet, can i use the same bc that i came up with and just adjust all the other info?

Thanx alot guys, and i am open to any input or ideas how how you do yours.

Clayne_b

 

[Lowlight]

Re: Drop charts

Yes and No,

It depends what you are shooting and how far and what you are using for a program to create your drop chart.

Biggest difference I see above 9,000 ft is the windage adjustment. The elevation changes for sure but the windage necessary really changes.

Putting in my data the elevation is usually pretty darn good providing your using real time information for the weather. I recommend investing in a good ballistic computer to take with you.

 

[Woj8541]

Re: Drop charts

Calculating a BC from drop or time of flight isn't the best way to go. I recommend using an experimental BC and sticking with that, no matter what. The BC is telling the computer how that particular projectile flies through the air. When you input the atmospherics into the computer, the algorithms do the rest. G1 BC's will vary with velocity, but G7 BC's will only vary a couple percent one way or another.

My suggestion is to chrono your ammo and input accurate atmospherics taken at the time of zeroing/chronoing into the computer under "zero atmosphere" or while developing a weapon profile, whichever way your particular system is formatted. Once you do that you can input various atmospheric conditions that will reflect the conditions you'll experience while you're on your hunt. The computer will automatically calculate those solutions based off of your zeroing conditions.

Frank hit it well on the wind, as most people don't take into account that as the air becomes less dense it takes an effect on both elevation as well as wind deflection. Make sure you study both profiles on your charts. Don't think that a 10 MPH wind is "X" mils at 600 yards at 2500 ft MSL will have that same "X" mil value at 11,000 ft msl. You'll miss, or worse, make a poor shot.

Getting a portable ballistic solver is a very smart choice. Best luck on your hunt.

 

[pius]

Re: Drop charts

hey i was wondering how do u dope on a scope for example 12.8 moa how do u dope the .8 some 1 help me

 

[Lowlight]

Re: Drop charts

What scope, there are scopes that adjust in 1/8 minute, 1/4, 1/2, or even 1 MOA.

 

[clayne_b]

Re: Drop charts

30 06, barns vortx 180gr

4700ft
temp 72
pressure 25
humid 33

muzzle 2709 5 shot average
100 yards 2499 5 shot average

 

[clayne_b]

Re: Drop charts

bushnel 3200 10x mildot

 

[Lowlight]

Re: Drop charts

On the home page of the site is a link to JBM Ballistics, a free online calculator.

Input your information, and for the weather I would not go much above 40 degrees, 50% humidity and then let the Baro stay at 29.92 and change the altitude to 4500, then calculate, after you print change the altitude to 10,500 (make sure you check the standard atmosphere at altitude box for both) and see what the differences are. That will help you determine a base line difference. (Include your home range calculations at 72 degrees too)

Odds are you are not going to be shooting too far, unless you liked to hunt beyond a certain distance like 350 yards, then if so, you are back to a real time portable calculator.

Inside 350 yards you won't be off by much, less than 1 MOA. After that, the changes will get bigger, as well, adding in angles will certainly add to the things that need be accounted for.

The scope part was for the other guy stepping on your thread.

 

[clayne_b]

Re: Drop charts

here is what i came up with in the field, with a laptop

 

[Lowlight]

Re: Drop charts

That data looks wrong, I don't think you inputted correctly.

I need to see the whole thing, I'm not a 30-06 guy but doesn't look right to me.

I'm thinking 14 MOA to 600 not 40

 

[clayne_b]

Re: Drop charts

what do you figure the BC is

muzzle 2706
100 yard 2499
30 06 180gr

temp 72
humidity 35
pressure 25

 

[clayne_b]

Re: Drop charts

my first bc i figured was .104 reloaded my info and got .299 and this is how the chart looks

 

[Lowlight]

Re: Drop charts

You need to use the library or look it up, a quick search, and think the BC is .453 G1

Garbage in, garbage out. It's in the JBM library

 

[ctressler]

Re: Drop charts

The G1 BC is .453 according to Barnes. However, some really good testing by Bryan Litz is published in his book Applied Ballistics and he has a slightly more accurate BC, so you need to buy his book and use that BC.

The BC does change at different altitude because the velocity of the bullet will be faster/slower given the density of the air. The BC isn't changing because of the altitude, it scales with velocity.

You have been given some good feedback from Lowlight and Caylen W, I would suggest getting your hands on a copy of Bryan Litz book if you really want to understand ballistics.

I have a really good friend that lives in Saratoga Springs, I used to shoot rabbits there when it was just sage brush.