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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
McWhorter Rifles 6.5 Wby Mag.!!
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<blockquote data-quote="AJ Peacock" data-source="post: 292860" data-attributes="member: 4885"><p>I don't doubt it at all, Quickload shows that 3275fps in the 270wby and 140gr bergers will give a pressure of around 66k psi. Definitely a good solid and safe load in a strong rifle. The question would be when necking it down and loosing the efficiency, how high would the pressure be. </p><p></p><p>Lets look at an example of necking down a cartridge and comparing it's performance to it's parent with the same weight bullet and same pressure. Looking at the 308win and 7mm-08 velocities and pressures with the same weight bullet shows the loss in efficiencies. I looked at the 150gr numbers for both cartridges and the 7mm-08 looses about 5% velocity for the same pressure and weight bullet from it's parent the 308Win. Necking the .308 down to .284 is a reduction of 15% in bore area. Necking the 270 down to 264 is a reduction of around 14%, so the numbers should be relevant.</p><p></p><p>If the loss in velocity for the same weight bullet and same pressure is 5%, then the 264x270wby and a 140gr bullet should be around 3111fps (using your velocity in the 270wby). The 264Win Mag and the 140gr bullet shows a velocity of 3170fps when the pressure is 66k psi.</p><p></p><p>Just some numbers to ponder,</p><p>AJ</p></blockquote><p></p>
[QUOTE="AJ Peacock, post: 292860, member: 4885"] I don't doubt it at all, Quickload shows that 3275fps in the 270wby and 140gr bergers will give a pressure of around 66k psi. Definitely a good solid and safe load in a strong rifle. The question would be when necking it down and loosing the efficiency, how high would the pressure be. Lets look at an example of necking down a cartridge and comparing it's performance to it's parent with the same weight bullet and same pressure. Looking at the 308win and 7mm-08 velocities and pressures with the same weight bullet shows the loss in efficiencies. I looked at the 150gr numbers for both cartridges and the 7mm-08 looses about 5% velocity for the same pressure and weight bullet from it's parent the 308Win. Necking the .308 down to .284 is a reduction of 15% in bore area. Necking the 270 down to 264 is a reduction of around 14%, so the numbers should be relevant. If the loss in velocity for the same weight bullet and same pressure is 5%, then the 264x270wby and a 140gr bullet should be around 3111fps (using your velocity in the 270wby). The 264Win Mag and the 140gr bullet shows a velocity of 3170fps when the pressure is 66k psi. Just some numbers to ponder, AJ [/QUOTE]
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McWhorter Rifles 6.5 Wby Mag.!!
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