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# Math for dummies/noobies

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#1
04-03-2009, 02:07 AM
 Junior Member Join Date: Mar 2009 Location: FT. Collins CO Posts: 28
Math for dummies/noobies

I have searched for info on a few questions and came up with half the answers so I will ask it here in hopes some one can fill in the blanks or straighten me out.

1st question - effect of temperature on POI, I know this is gonna be a lil different for every bullet/gun etc. But is their a general rule of thumb for rough estimation to start with? 1 guy on another site said he loses 1 moa @ 1,000 yd for every 10* decrease in temp? Is that a good estimate? What about 500 yds? Mainly looking for like 40*F - 100*F any colder then that I am on the couch!

2nd question - Wind drift, I know you can use the ballistics programs to get this if you have all your bullet info, I seen on another site you square it, say if your off 1" @ 100yds with a 10 mph crosswind it would be 100" @ 1,000 yds (rough estimate)?

3rd question - barometric pressure effect. I have spent alot of time reading about rain/temp/altitude/pressure tonight, the altitude's I will be shooting at are quite different so that will be easy to dope, what about pressure? Is their a rule of thumb for adjusting?

Just looking for some starter info to know where to start. Thanks for any help to get me started.
#2
04-03-2009, 07:41 AM
 Platinum Member Join Date: Jun 2001 Location: Potomac River Posts: 5,089
Re: Math for dummies/noobies

The thing I do is to go to JBM

JBM - Calculations - Trajectory

Question #1 - Then I run my ballistics at different temperatures keeping everything else the same. I cut and paste the data into a word document because my memory is not good enough to keep track of that many numbers all at once. I can then find out what the change is at what ever distance I wish.

Question #2 Run your bullet and see what JBM gives you.

Question # 3 Do the same as question #1 except this time change altitude by 1000 feet and see what the difference is.

In case you think I have not answered your question you are right. You have to learn how to use a ballistics program just like all the rest of us.
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#3
04-03-2009, 10:12 AM
 Junior Member Join Date: Mar 2009 Location: FT. Collins CO Posts: 28
Re: Math for dummies/noobies

I just wanted to know if their was a way to figure it out with out the program. May not always have the notebook with me you know.
#4
04-03-2009, 04:32 PM
 Platinum Member Join Date: Mar 2007 Location: MN Posts: 1,219
Re: Math for dummies/noobies

BB is right. There is no accurate "rule of thumb" because LRshooting is all about accuracy. wind drift has to do with arrow dynamics and velocity. Ballistic Coefficient will determine how fast the bullet will slow down and every different bullet has a different BC. look at a 22-250 40grain pushing 3900 fps that will have minimal wind deflection at 200 yards but a whole heck of a lot at 700. Now compare to a 300 win mag pushing a higher BC bullet at around 3000fps that will have slightly more at 200 but way way less at 700.

Long story short, there is no simple way to be right on. Just make a drop chart and a wind chart and go from there. One general rule of thumb is that if you have a chart set up for 10 mph winds and you are experiencing 5 mph, you cut your numbers in half. If you are experiencing 15 mph winds, you multiply your drift by 1.5. 20mph... x2 and so on.

hope this helps, Mark.
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I used to re-load but now I "hand-load".
-- Well, at least I try --
#5
04-04-2009, 12:23 AM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,830
Re: Math for dummies/noobies

What you need is a pocket PC with pocket excel and my ballistic calculator that you take to the field. It factors everything you need to make an ACCURATE shot at long range without having to guess. You will also need a small wheather meter to get temp and pressure. Altitude is of no concern as you would use raw pressure regardless of altitude.
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
#6
04-05-2009, 05:05 AM
 Silver Member Join Date: May 2008 Location: NEW ZEALAND Posts: 208
Re: Math for dummies/noobies

At the very least crony and colate a drop chart using JBM, print it off and go shoot some rocks at the ranges, you will be surprised!

You will need to take a note book and pen to make notes of impact points, yes this sounds very gay,shirt lifting type of behavoiur,BUT you will need to recall ALL the changes you have made from your initial table to get one thats more your load/rifle/your position etc specific.

its been said before Long range hunting is all about the math, did you ever go to math class without a pen and pad??

You dont need yet but it will happen!a weather station and some form of portable balistic calculator but for now pieces of paper will be ok

My only piece of wisdom I can empart "windage is only half of what you think it is"
dont knock it till youve tryd it you may find im right, I even half what Exbal tells me and it aint gone wrong yet.
Probly compensating for my flinch LOL!!!

Oh yes and go and order Shawn Carlocks DVD and watch that half a dozen times too.

All the best

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