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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
ballistic coefficients?
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<blockquote data-quote="Jeff In TX" data-source="post: 27957" data-attributes="member: 1522"><p>Here's the real issue when it comes to BC's. Bullet manufactures use a G1 drag coefficient. The G1 drag coefficient and the mathematical calculations were developed for flat nose projectiles such as the 45 ACP bullets. The G1 Drag yields high BC numbers. </p><p></p><p>Boat tail bullets use the G5 drag model. The G5 drag model and the mathematical calculations were developed specifically for boat tail bullets, but they produce a lower BC numbers because of the mathematical calculations involved. VLD (Very Low drag) bullets use the G7 drag model and flat base spire point bullets use the G6 drag model. </p><p></p><p>Bullet manufactures advertise the G1 drag model because of the higher BC number. Higher BC's sell more bullets. The Sierra .308 168 gr, match king has an advertised G1 BC of .462. The actual G5 drag BC is .289. This is the drag model the US Army uses at the Aberdeen Proving grounds for its calculations. Why, because it is very accurate.</p><p></p><p>Most of the ballistic programs on the market use the G1 drag model and out past 450 yards the accuracy starts to slide down hill quickly. Some of the better programs such as Ohler still use the G1 drag model, but have massaged the mathematical calculations for better accuracy.</p><p></p><p>My ballistic program is near dead on to 800 yards for my .308. That is if I input all of the correct data. Beyond that it's a matter of the me or the ballistic program as to what's really correct, but were not off by much.</p></blockquote><p></p>
[QUOTE="Jeff In TX, post: 27957, member: 1522"] Here’s the real issue when it comes to BC’s. Bullet manufactures use a G1 drag coefficient. The G1 drag coefficient and the mathematical calculations were developed for flat nose projectiles such as the 45 ACP bullets. The G1 Drag yields high BC numbers. Boat tail bullets use the G5 drag model. The G5 drag model and the mathematical calculations were developed specifically for boat tail bullets, but they produce a lower BC numbers because of the mathematical calculations involved. VLD (Very Low drag) bullets use the G7 drag model and flat base spire point bullets use the G6 drag model. Bullet manufactures advertise the G1 drag model because of the higher BC number. Higher BC’s sell more bullets. The Sierra .308 168 gr, match king has an advertised G1 BC of .462. The actual G5 drag BC is .289. This is the drag model the US Army uses at the Aberdeen Proving grounds for its calculations. Why, because it is very accurate. Most of the ballistic programs on the market use the G1 drag model and out past 450 yards the accuracy starts to slide down hill quickly. Some of the better programs such as Ohler still use the G1 drag model, but have massaged the mathematical calculations for better accuracy. My ballistic program is near dead on to 800 yards for my .308. That is if I input all of the correct data. Beyond that it’s a matter of the me or the ballistic program as to what’s really correct, but were not off by much. [/QUOTE]
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