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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
G1... G7... ??
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<blockquote data-quote="Jeff In TX" data-source="post: 337244" data-attributes="member: 1522"><p>Robster, the G8 is for a flat base VLD not a boat tail VLD bullet.</p><p></p><p></p><p></p><p>Mark,</p><p></p><p>Dang you I knew sooner or later someone would ask that question and open a whole new can of worms. The long and short of it, each bullet needs to be measured and tested to see what coefficient drag model it fits into. There's not a one size fits all and the hope is bullet manufactures would step and provide this information for the shooter.</p><p></p><p>Berger has essentially started this with Bryan publishing the G7 BC's for their bullets as well as many other bullets. But as I stated Berger's bread and butter bullets are their VLD bullets so they fall nicely into the G7 coefficient drag model.</p><p></p><p>We'll not likely get this support or information out of Sierra any time soon. They like the higher BC's of the G1 drag model…"marketing tool"! Also their ballistic program massages the G1 calculations by using multiple G1 BC's across different velocities to get more accurate results. IMHO this is poor idea and just a band-aid trying to get an obsolete G1 drag model to more accurately predict bullet flight using their ballistic program. The real issue is how you accurately measure the multiple BC's over those different velocities? Also the G1 BC can change gun to gun (barrel to barrel) depending on bore diameter, twist rate and barrel length. So it's a crap shoot at best.</p><p></p><p>I use the RSI Ballistic Lab program and it has a drag modeling tool for determining the correct drag model. It works really well for me. I spend a lot of time working ballistic calculations. I also spend a lot of time tweaking my ballistic program inputs. I can get my ballistic program to match my actual shooting data very accurately. In the end it comes down to the data you input into your ballistic program that determines the output data. Understanding how everything works together and what inputs conflict with other inputs can determine just how accurate your results can be.</p></blockquote><p></p>
[QUOTE="Jeff In TX, post: 337244, member: 1522"] Robster, the G8 is for a flat base VLD not a boat tail VLD bullet. Mark, Dang you I knew sooner or later someone would ask that question and open a whole new can of worms. The long and short of it, each bullet needs to be measured and tested to see what coefficient drag model it fits into. There’s not a one size fits all and the hope is bullet manufactures would step and provide this information for the shooter. Berger has essentially started this with Bryan publishing the G7 BC’s for their bullets as well as many other bullets. But as I stated Berger’s bread and butter bullets are their VLD bullets so they fall nicely into the G7 coefficient drag model. We’ll not likely get this support or information out of Sierra any time soon. They like the higher BC’s of the G1 drag model…”marketing tool”! Also their ballistic program massages the G1 calculations by using multiple G1 BC’s across different velocities to get more accurate results. IMHO this is poor idea and just a band-aid trying to get an obsolete G1 drag model to more accurately predict bullet flight using their ballistic program. The real issue is how you accurately measure the multiple BC’s over those different velocities? Also the G1 BC can change gun to gun (barrel to barrel) depending on bore diameter, twist rate and barrel length. So it’s a crap shoot at best. I use the RSI Ballistic Lab program and it has a drag modeling tool for determining the correct drag model. It works really well for me. I spend a lot of time working ballistic calculations. I also spend a lot of time tweaking my ballistic program inputs. I can get my ballistic program to match my actual shooting data very accurately. In the end it comes down to the data you input into your ballistic program that determines the output data. Understanding how everything works together and what inputs conflict with other inputs can determine just how accurate your results can be. [/QUOTE]
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G1... G7... ??
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