Advanced Marksmanship Formula for Calculating MV?

[George Collins]

Wow, I feel like I've hit the big-time cause here I am posting in the "Advanced Maksmanship" section.  

Now to make a fool of myself. 

I was at the range earlier today and squeezed a few off. I ran a ballistics table on the load I was using but since we forgot the dad-blamed blankety-blank chronograph, I had to SWAG the MV into my iPhone App/JBM calculator. I noticed that dopes based on the ballistics table were consistently and pervasively high. 

The first yard line I shot from was the 300 as this is my zero range. Once the range card value for the 300 was observed and recorded, the process was repeated at the 400. Then at the 500, by coming up the exact amount suggested by my SWAGed ballistics table, the bullet was damn nigh off'n the paper (perhaps bigger paper?). 

It was here that I got sick and came home. I mean literally sick. Temperature was like 100.8. 

As I lay here convalescing (and moaning and bemoaning), I kept replaying my day at the range in my feverish forebrain and a mathematical idea snuck in. (You know you're a sick puppy when . . . ). 

Here's the invasive weed of an idea that has been plaguing my delerium - if BC, bullet weight, etc., is known and if elevation corrections are accurately made at two or more known distances, can a MV be accurately derived?

And if it can arrived at in such a backwards way, what is the method of its derivation?

Thank you in advance for any help provided and IF you actually provide help, I will thank you again after the fact. 

 

[Fred_C_Dobbs]

Re: Formula for Calculating MV?

The cheapest way to figure it without giving yourself a brain cramp is to use the JBM's online calculator and keep plugging in different values for MV until its predicted drop matches your range data.

 

[George Collins]

Re: Formula for Calculating MV?

Fred,

Thank you for your reply but I did that already and the results were helpful.

However, I'm one of those silly individuals that enjoy brain cramps, ass whuppins and joining the Marine Corps.

I was hoping for the long-hand version.

I have researched extensively online since making this post. The only thing I have found thus far is the name of this technique for obtaining MV:

The POI method.

A brief description of the POI method can be found here. However, I don't want a computer program to do the work for me. I was hoping to wrestle with the figures myself so that there might be another usable tool in the ol' box iffn there might ever come a time when one might be called upon to shoot a strange load and unable to access a computer.

 

[Fred_C_Dobbs]

Re: Formula for Calculating MV?

Sorry 'bout that, Tarzan. My math skills are overtaxed by balancing my checkbook.

To quote President Carter when he announced the Soviet missiles were en route to the US, "Thank you very much, you're on your own." ;-)

 

[sobrbiker883]

Re: Formula for Calculating MV?

I use the "tweaking JBM until it matches real world data" method. Then I make data cards for different DA's off off my known conditions and they work like a charm.

This has worked much better in practical application than trusting chronos and trying to make reality match what extravagent interpolation tells me it should be.

Closest thing to an "Easy Button" we have as shooters.

If you want the brain cramp, summon the ArcanaMaven by chanting his name thrice......

 

[George Collins]

Re: Formula for Calculating MV?

Perhaps a different question then:

The JBM calculator uses some formula for being able to calculate the drop of a bullet iffn one plugs in MV, BC, bullet weight, zero range, coriolis effect and spin drift direction and anticipated magnitude divided by the parallax error for having been astigmatized in the 6th grade.

Does anyone know the formula that JB uses to deduce his set of figgers given the above listed variables (give or take a few)?

 

[MALLARD]

Re: Formula for Calculating MV?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TallahallaTarzan</div><div class="ubbcode-body">Now to make a fool of myself. </div></div>
hahaha
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TallahallaTarzan</div><div class="ubbcode-body"> is known and if elevation corrections are accurately made at two or more known distances, can a MV be accurately derived? </div></div>
i cant recommend you do that , its all to likely your other "knowns" are incorrect , even if its wrong by alittle it can have big effect when using a ballistic program

there is really no way you can accurately measure the BC of the rounds your firing ( unless you got some fancy shit) , and BC round to round varies enough to have an effect on the ballisitic program, that in combination with ES/SD , the wind speed/wind gradient , possible errors in your scope tracking, ect in my eyes rules out accurately deriving your m/vs from a backwards method.

not to say i have faith in the chrony , even if i did that won't account for the other things i mentioned

at a short range this wouldnt matter , at a longer range it would have a noticeable effect

i really like how your thinking though , i just think its an uphill battle, but hey i maybe wrong.

 

[maladat]

Re: Formula for Calculating MV?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TallahallaTarzan</div><div class="ubbcode-body">Does anyone know the formula that JB uses to deduce his set of figgers given the above listed variables (give or take a few)?</div></div>

It's not "a formula."

It is a system of differential equations which are numerically integrated over time to find the solution.

You can't just solve out muzzle velocity.

There is a closed form analytical solution of the much simpler, much less accurate Siacci equations here (still plenty complicated):

http://www.exteriorballistics.com/ebexplained/4th/65.cfm