Stupid questions - math lesson

[ez bake]

I've been playing with ballistics software for a little while now and trying to get some guesstimates together to take a couple of different rounds out to 1000yds and get some real measurements with a couple of newer rounds I'm trying out. I understand most of what I'm reading (or at least I can fake it), but how is trajectory measured? I keep seeing these numbers in my charts and in the software and I have no idea what the heck they mean (I've googled a couple of things, but can't find much that dumbs it down for me).

Also, if I've figured my come-up for various distances in MOA, and I try and convert that number to Mils for holdover, it doesn't ever equal the same thing that the software converts it to (I'm assuming this is because I'm using 3.5 as a guess where the software is either using 3.438 or 3.6?).

I've now read mathematical answers as to why a Milradian could be either3.44 or 3.6 (rounded) in MOA, but I'm not sure which is the more trusted (so I did what a lot of sites suggested and split the difference to 3.5). This isn't working out very well so far as I have to keep cheating by using my software to double-check what I'm getting in my own math.

 

[ez bake]

I think I found the answer to my second question - 3.44 is the correct guesstimate (1 milliradian = 3.438 is the better answer?). My conversions are closer, but not quite there yet (unless my math is off - isn't 1 mil equal to 3.438 MOA?)

There are 2pi radians in a circle. 2*pi = 6.2832. Therefore, there are 6,283.2 milliradians in a circle. This equates to 3.44 MOA per milliradian, or distance between two mil dots.

However, the military decided to change this measurement in the context of a military compass to reflect 6,400 milliradians in a circle. This resulted in 1 milliradian equaling 3.6 MOA instead of 3.44 MOA.

So, the military didn't simply "adopt" the geometry. They in fact changed it. Thus the term "military geometry," because in actual geometry, there are only 6,283.2 mil rads in a circle, not 6,400.

 

[Rod Snell]

I think I found the answer to my second question - 3.44 is the correct guesstimate (1 milliradian = 3.438 is the better answer?). My conversions are closer, but not quite there yet (unless my math is off - isn't 1 mil equal to 3.438 MOA?)

Just a general comment on doing calculations using natural constants like pi and natural logarithms (ln).
The numbers are infinitely long, and you are only using approximations. The scientific calculators that carry the natural constant values internally out to 12 places are much better approximations than the truncated ones, and give better answers. It is better to hit the "pi" key on the scientific calculator than to enter 3.14159.

 

[ez bake]

Just a general comment on doing calculations using natural constants like pi and natural logarithms (ln).
The numbers are infinitely long, and you are only using approximations. The scientific calculators that carry the natural constant values internally out to 12 places are much better approximations than the truncated ones, and give better answers. It is better to hit the "pi" key on the scientific calculator than to enter 3.14159.

That's what I'm hoping is happening. Still, I have no idea as to what the trajectory numbers mean (here's an example from Hornady's online ballistic calculator):

http://www.hornady.com/cgi-bin/ball...om=29.53&zero=100&wspd=0&calcbutton=Calculate

 

[Beercules]

That's what I'm hoping is happening. Still, I have no idea as to what the trajectory numbers mean (here's an example from Hornady's online ballistic calculator):

http://www.hornady.com/cgi-bin/ball...om=29.53&zero=100&wspd=0&calcbutton=Calculate

The trajectory numbers are how far above or below the bullet is from your line of sight. The MOA conversion for holdover has been done for you, but you can see the correlation with the trajectory numbers.

 

[MoBoost]

See if this helps: http://www.shooterready.com/lrsdemohi.html

 

[ez bake]

See if this helps: http://www.shooterready.com/lrsdemohi.html

Yeah - I've actually done that simulation and considered ordering the CD from them. That's a good site.

And Beercules - I get that the trajectory numbers are how far above or below the bullet is from your line of sight, but what the heck is it measured in (doesn't look like degrees)? I can't seem to convert from MOA to get the Trajectory numbers and a lot of software out there has trajectory numbers listed at different distances and I'd just love to know how to get from one measurement to the other.

I gotta be honest, if someone would have told me in high school that I would be studying geometry and trig as an adult and actually liking it I would have said they were crazy.

 

[MoBoost]

Most software will put out (hehe, I said put out) POI in inches. For simplicity 1 inch at 100 yards is 1 MOA.


Simplified formula : (POI in MOA) = (POI in IN) * 100 / (Distance in YARDS)

1/4MIL is 1MOA rounded up (.9 to be exact)

The software says you are 4" high at 100 yards - that's 4 MOA high - 1 MIL high.
The software says you are 16" low at 400 yards - that's 4 MOA low - 1 MIL low.

 

[ez bake]

Most software will put out (hehe, I said put out) POI in inches. For simplicity 1 inch at 100 yards is 1 MOA.


Simplified formula : (POI in MOA) = (POI in IN) * 100 / (Distance in YARDS)

1/4MIL is 1MOA rounded up (.9 to be exact)

The software says you are 4" high at 100 yards - that's 4 MOA high - 1 MIL high.
The software says you are 16" low at 400 yards - that's 4 MOA low - 1 MIL low.

So the trajectory numbers are poi in inches at those distances?

 

[ez bake]

Most software will put out (hehe, I said put out) POI in inches. For simplicity 1 inch at 100 yards is 1 MOA.


Simplified formula : (POI in MOA) = (POI in IN) * 100 / (Distance in YARDS)

1/4MIL is 1MOA rounded up (.9 to be exact)

The software says you are 4" high at 100 yards - that's 4 MOA high - 1 MIL high.
The software says you are 16" low at 400 yards - that's 4 MOA low - 1 MIL low.

OK - so I'm getting close to those numbers by taking come-up in MOA and multiplying by 1.047 to get inches and then multiplying by 1/100 of whatever the yardage is at the various places on the chart to get my poi in inches.

But I'm totally unable to do the same thing with wind drift (with any degree of accuracy) so I thought I was converting wrong. I must be doing something else wrong.

Once I've figured out (what I think is) the wind-speed, I then look at the drift on the range card (which is only in inches per 1mph in a couple of the simulators I'm using) and multiply that number by what I think is the wind-speed in MPH. I then take that number and divide by 1.047 and then by 1/100 of the yardage to get my adjustment in MOA and my POI is always waaaaaay off (yet my guess at the wind-speed is always fairly close).