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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Hunting with a Marginally Stable Bullet
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<blockquote data-quote="Hugnot" data-source="post: 2644149" data-attributes="member: 115658"><p>Your 7mm ELDX will have more than adequate of a Sg for its intended use. This is <u>not</u> a marginally stable bullet for your specific use.</p><p></p><p>The Berger Sg calculator, that was used to come up with a Sg of 1.38, does not make allowances for plastic tipped bullets like the Hornady .284 ELDX. The plastic tips are regarded as having zero mass by the Miller Sg estimator that is used by JBM & others. The Berger Sg estimator will give low Sg values because the plastic tip is regarded has having the same mass as the entire bullet. When applying the bullet OAL to the Berger Sg estimator the Sg process assumes that the entire bullet does not have a plastic tip and the Miller Sg process used by JBM & others subtracts the plastic tip from the bullet OAL. This means no problem for your intended use - your 7mm 175 ELDM bullets will fly good with nice Sg's. Sg values will increase as range increases.</p><p></p><p>The Berger Sg calculator uses Hg pressures commonly found at certain altitudes and does not compensate for atmospheric conditions like high pressure "blue bird" days or stormy humid days. The Berger Sg calculator uses the common Miller Sg estimator but does not allow for atmospheric conditions that would affect pressure or plastic tips that are regarded as having no mass but are included in bullet OAL.</p><p></p><p>So:</p><p></p><p>[ATTACH]403241[/ATTACH]</p><p></p><p>[ATTACH]403242[/ATTACH]</p><p></p><p>The 7mmSTW sounds like some kind of cannon, I guessed it would shoot 175's at 3000 fps. If I had to shoot deers I would use my little 6mm CM. The 7mm STW sort of looks like a scaled down version of the US Navy 3 inch 50 or Germainian 88 - big guns for shooting hi altitude aircraft or armor fiercing.</p><p></p><p></p><p>The spread sheet contains 3 columns each having 3 different pressures or altitudes (sea level, 3000 ft, 5000 ft) & two rows of 35 & 45 temperatures. The math is shown at the top & the operation where plastic tip length (.142) is subtracted for OAL is shown (column & row).</p><p></p><p>The altitude & pressure chart provide pressures at certain altitudes.</p><p></p><p>Your use of the 7mm ELDX would be close to optimum for shooting deers up to 500 - good Sg, good terminal stuff, good wind & trajectory. Lots of effective smashing terminal stuff to kill the deers.</p><p></p><p>Use the Hornady 4DOF calculator instead of the Berger. The Hornady 4DOF indicates adequate stability for your application.</p><p></p><p>[URL unfurl="true"]https://www.hornady.com/team-hornady/ballistic-calculators/#!/[/URL]</p></blockquote><p></p>
[QUOTE="Hugnot, post: 2644149, member: 115658"] Your 7mm ELDX will have more than adequate of a Sg for its intended use. This is [U]not[/U] a marginally stable bullet for your specific use. The Berger Sg calculator, that was used to come up with a Sg of 1.38, does not make allowances for plastic tipped bullets like the Hornady .284 ELDX. The plastic tips are regarded as having zero mass by the Miller Sg estimator that is used by JBM & others. The Berger Sg estimator will give low Sg values because the plastic tip is regarded has having the same mass as the entire bullet. When applying the bullet OAL to the Berger Sg estimator the Sg process assumes that the entire bullet does not have a plastic tip and the Miller Sg process used by JBM & others subtracts the plastic tip from the bullet OAL. This means no problem for your intended use - your 7mm 175 ELDM bullets will fly good with nice Sg's. Sg values will increase as range increases. The Berger Sg calculator uses Hg pressures commonly found at certain altitudes and does not compensate for atmospheric conditions like high pressure "blue bird" days or stormy humid days. The Berger Sg calculator uses the common Miller Sg estimator but does not allow for atmospheric conditions that would affect pressure or plastic tips that are regarded as having no mass but are included in bullet OAL. So: [ATTACH alt="Screenshot (501).png"]403241[/ATTACH] [ATTACH alt="Screenshot (499).png"]403242[/ATTACH] The 7mmSTW sounds like some kind of cannon, I guessed it would shoot 175's at 3000 fps. If I had to shoot deers I would use my little 6mm CM. The 7mm STW sort of looks like a scaled down version of the US Navy 3 inch 50 or Germainian 88 - big guns for shooting hi altitude aircraft or armor fiercing. The spread sheet contains 3 columns each having 3 different pressures or altitudes (sea level, 3000 ft, 5000 ft) & two rows of 35 & 45 temperatures. The math is shown at the top & the operation where plastic tip length (.142) is subtracted for OAL is shown (column & row). The altitude & pressure chart provide pressures at certain altitudes. Your use of the 7mm ELDX would be close to optimum for shooting deers up to 500 - good Sg, good terminal stuff, good wind & trajectory. Lots of effective smashing terminal stuff to kill the deers. Use the Hornady 4DOF calculator instead of the Berger. The Hornady 4DOF indicates adequate stability for your application. [URL unfurl="true"]https://www.hornady.com/team-hornady/ballistic-calculators/#!/[/URL] [/QUOTE]
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