Re: Plotting Bullet Ogive shape on a graph
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lou Boyd</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Country</div><div class="ubbcode-body">Dose anyone know what kind of Windows based program I need to plot the shape of a bullet ogive as a graph . I know how to measure the ogive with a dial gauge in the lathe but I need to know what program to enter the measurements into to get an accurate representation of the ogive shape . I need to do this for some bullets I make that I am not sure what ogive they actually are.
I tried it in Microsoft Excel and got a graph of an ogive shape but the radius of the ogive depicted changed as I changed the number of measured points along the ogive , that is the distance between each dial guage measurement along the ogive .
With 10 sample points I got one size ogive and with 20 sample points on the same bullet , another bigger curve .
I would appreciate some assistance if anyone has already worked this out. </div></div>
Drafting Computer Aided Design (CAD) programs can make precise drawings from numeric measurements. The popular industrial versions like Autocad or SolidWorks are very expensive, but there are some freeware and/or demo versions of cad programs which can do the job. I use an antique DOS version of Autocad and qcad under Linux. (GNU free license).
A quick search for "free windows drafting software" found this and others. I haven't used it.
http://www.graytechsoftware.com/products/cadx11/index.asp I measure bullet and brass dimensions by mounting a USB CCD camera with a telecentric lens on my milling machine and use the table digital readouts (DRO) which have 0.0002" resolution to make the measurements.
I can also take a high resolution image of the bullet and count pixels to get dimensions. It's not as precise but faster for complex shapes.
The advantage of the cad software is that you can enter points from measurements and then use the software to fit curves to determine radiuses. Most Cad programs do that easily.
I generally just use the data to get the bullet OAL and the position of the shank for manufacturers who don't provide that information for their bullets. I've not had much luck trying to calculate BCs or stability from measurements using McCoy's equations. The problem is not knowing the internal mass distribution. The measurements are useful for designing handloads but not of as much use for predicting performance as shooting tests.
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Thanks Lou Boyd , So it's a CAD program I need . That sounds exactly what I want . To be able to produce the curve and fit known radius curves against it to determine the actual ogive radius I have . Internal bullet construction is not a problem as I make them from scratch anyway . I will give that link a go and see what I can download . Thanks mate , not being an engineer I have not had any experience with CAD stuff so had no idea of what it could do . Some of my bullet swaging gear was bought from a deceased estate and the sellers did not have a clue what it all was anyway , got $5000 worth of die sets and presses , core moulds , jacket drawing dies and thousands of jackets for $500 !! a few of the point forming dies are not marked with the ogive radius . It is real hard to tell an 8 ogive from a 9 by eye . I have been shooting a 6mm .243 bullet I make for years and thought it was an 8 ogive but recently worked out it is closer to a 10 ogive . The difference did not make much difference to the calculated trajectory but it did bring the calculated trajectory closer to the actual real world drop on the target. So I decided I want to know how to measure the ogive shape accurately .
