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The Basics, Starting Out
Drag functions and drop charts
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<blockquote data-quote="Mysticplayer" data-source="post: 113028" data-attributes="member: 8947"><p>The Drag or G function describes the type of bullet you use. I tried to find the definitions but my link no longer works. Flat base, Boat tail, Secant ogive, VLD are just a few of the broad categories that bullets fall into.</p><p></p><p>Each one is represented by a G function.</p><p></p><p>The BC is simply a number which illustrates the value for that G function. Can only be used to compare relative drag between bullets of the same G family.</p><p></p><p>Example a G5 bullet with 0.700BC will have less drag then a G5 bullet with a 0.500BC.</p><p></p><p>Without knowing what G function was used to generate the BC, it really is meaningless.</p><p></p><p>That is why some bullets fly substantially flatter despite having the same BC. The two bullets differ in G function which really defines how that bullet decelerates in flight.</p><p></p><p>Example a G1 bullet with a BC of 0.500 will not fly anywhere as flat as a G7 bullet with the same BC of 0.500.</p><p></p><p>The link will bring you to a site which has a ton of info on ballistics. Also, let's you generate drop charts and play with your data.</p><p></p><p>Unfortunately, there are no rules throughout the bullet industry to standardise the BC values. Some inflate their printed values to make their bullets look good. Others under estimate because the bullet follows a better drag function.</p><p></p><p>Some like Sierra give their BC's through shooting the bullets. Others just use the number that squirts out from a bullet form program.</p><p></p><p>Most BTHP match bullets follow a G5 function. Some poly tipped BT match bullets and VLD bullets follow the G7 drag function.</p><p></p><p>Also, bullets can change their relative G function and BC depending on the distortion incurred while travelling down the bore or at the velocities launched.</p><p></p><p>Confusing...You bet.</p><p></p><p>What I do is use a ballistics program to generate a drop chart. Use whatever printed data is given. This will get me close. I then make up a 'true' drop chart based on real world shooting on several days.</p><p></p><p>Jerry</p><p></p><p><a href="http://www.eskimo.com/~jbm/calculations/calculations.html" target="_blank">http://www.eskimo.com/~jbm/calculations/calculations.html</a></p></blockquote><p></p>
[QUOTE="Mysticplayer, post: 113028, member: 8947"] The Drag or G function describes the type of bullet you use. I tried to find the definitions but my link no longer works. Flat base, Boat tail, Secant ogive, VLD are just a few of the broad categories that bullets fall into. Each one is represented by a G function. The BC is simply a number which illustrates the value for that G function. Can only be used to compare relative drag between bullets of the same G family. Example a G5 bullet with 0.700BC will have less drag then a G5 bullet with a 0.500BC. Without knowing what G function was used to generate the BC, it really is meaningless. That is why some bullets fly substantially flatter despite having the same BC. The two bullets differ in G function which really defines how that bullet decelerates in flight. Example a G1 bullet with a BC of 0.500 will not fly anywhere as flat as a G7 bullet with the same BC of 0.500. The link will bring you to a site which has a ton of info on ballistics. Also, let's you generate drop charts and play with your data. Unfortunately, there are no rules throughout the bullet industry to standardise the BC values. Some inflate their printed values to make their bullets look good. Others under estimate because the bullet follows a better drag function. Some like Sierra give their BC's through shooting the bullets. Others just use the number that squirts out from a bullet form program. Most BTHP match bullets follow a G5 function. Some poly tipped BT match bullets and VLD bullets follow the G7 drag function. Also, bullets can change their relative G function and BC depending on the distortion incurred while travelling down the bore or at the velocities launched. Confusing...You bet. What I do is use a ballistics program to generate a drop chart. Use whatever printed data is given. This will get me close. I then make up a 'true' drop chart based on real world shooting on several days. Jerry [url="http://www.eskimo.com/~jbm/calculations/calculations.html"]http://www.eskimo.com/~jbm/calculations/calculations.html[/url] [/QUOTE]
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