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Pressure/temp vs trajctory

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Unread 07-26-2004, 10:38 AM
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Re: Pressure/temp vs trajctory

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Unread 07-26-2004, 12:18 PM
JBM JBM is offline
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Re: Pressure/temp vs trajctory

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>PROBLEM: Correcting trajectory for measured barometric pressure and temperature to score first round hits without sighters.
Trajectories are to my understanding calculated according to a standard atmosphere. Change this and the bullet will behave differently and the calculated BC will change.

Yes it will. Also the speed of sound will change as a function of temperature and this will also affect the calculations (but not as much).

Don't forget the humidity correction (it is pretty small though).

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>
...then I can calculate the deviations (not correctly, but better than not doing it) by working out a new dropchart for the new BC.

It's not that bad -- but if you're calculating a new drop chart, you might as well just calculate one with new atmospheric conditions. If you meant that you're finding correction factors for the old chart, then keep in mind that the mach number is calculated using the conditions of the chart not the same conditions of the new BC.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>
I WANT: To find correction factors where I can correct directly from a trajectory chart without going the long way around and making a new one.<HR></BLOCKQUOTE>

Don't we all! Actually this has been my gripe with ballistics tables books that offer a bunch of tables. They're aren't much good when the conditions change. I'm working on some software to calculate the tables (just about done) and I am also developing some methods to correct the tables for different BCs, zero ranges and scope height. If I can find a publisher, I'll get it published. I don't really want to go the self publishing route. I hate hijacking threads, but is this something that might be useful (i.e. would you buy it)? I'd include the software so that you could make custom tables.
JBM Small Arms Ballistics --
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