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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Absolute Hammer actual vs Quick-load
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<blockquote data-quote="Carey Farmer" data-source="post: 2617534" data-attributes="member: 122715"><p>When I get a new barrel, after twenty break-in shots in the barrel, I calibrate QuickLoad Ba and weighting factor for the powder I plan to use. That is, I shoot a few different charge weights with a light-jacketed cup-and-core bullet, and back into a Ba and weighting factor that gives the best fit for charge weight vs muzzle velocity. I use the default starting pressure (3625 psi) for that calibration. Usually only small Ba changes, and no weighting factor changes, are needed to match Quickload predictions with measured muzzle velocities.</p><p></p><p>When the loads "speed up" (and they always do in my cut-rifled barrels), the only user-adjustable parameter that makes sense (to me) to change, to match QL to the higher muzzle velocity, is starting pressure. The powder hasn't changed. The weighting factor shouldn't change. The only thing that's changed is the condition of the bore. In particular the rifling is getting heat damaged and the lands are starting to retreat. Makes sense to me that a rough, burned surface of the rifling at the lands would increase starting pressure. </p><p></p><p>What I typically find is that after the barrel has sped up, and the lands have retreated 5 or 10 thousandths, for QL to match muzzle velocity (with new-barrel calibrated Ba and weighting factor) I have to use start pressures of 8000 - 9000 psi for thin-jacketed cup-and-core bullets (eg, ELD-X); 12000 - 13000 psi for heavy-jacketed hunting bullets (Accubond or Sierra TGK's); and even higher, up to 15,000 psi for Partition or Barnes bullets. I was pleasantly surprised to see that the Absolute Hammers only needed 10,000 psi starting pressure.</p><p></p><p>I don't know if those really are the starting pressures needed to get the bullets engraved. It could very well be that new-barrel starting pressures in cut-rifle barrels are actually below the defaults, and I should be calibrating Ba with lower starting pressures than the 3625 psi I use for thin-jacketed cup-and-core bullets.</p></blockquote><p></p>
[QUOTE="Carey Farmer, post: 2617534, member: 122715"] When I get a new barrel, after twenty break-in shots in the barrel, I calibrate QuickLoad Ba and weighting factor for the powder I plan to use. That is, I shoot a few different charge weights with a light-jacketed cup-and-core bullet, and back into a Ba and weighting factor that gives the best fit for charge weight vs muzzle velocity. I use the default starting pressure (3625 psi) for that calibration. Usually only small Ba changes, and no weighting factor changes, are needed to match Quickload predictions with measured muzzle velocities. When the loads "speed up" (and they always do in my cut-rifled barrels), the only user-adjustable parameter that makes sense (to me) to change, to match QL to the higher muzzle velocity, is starting pressure. The powder hasn't changed. The weighting factor shouldn't change. The only thing that's changed is the condition of the bore. In particular the rifling is getting heat damaged and the lands are starting to retreat. Makes sense to me that a rough, burned surface of the rifling at the lands would increase starting pressure. What I typically find is that after the barrel has sped up, and the lands have retreated 5 or 10 thousandths, for QL to match muzzle velocity (with new-barrel calibrated Ba and weighting factor) I have to use start pressures of 8000 - 9000 psi for thin-jacketed cup-and-core bullets (eg, ELD-X); 12000 - 13000 psi for heavy-jacketed hunting bullets (Accubond or Sierra TGK's); and even higher, up to 15,000 psi for Partition or Barnes bullets. I was pleasantly surprised to see that the Absolute Hammers only needed 10,000 psi starting pressure. I don't know if those really are the starting pressures needed to get the bullets engraved. It could very well be that new-barrel starting pressures in cut-rifle barrels are actually below the defaults, and I should be calibrating Ba with lower starting pressures than the 3625 psi I use for thin-jacketed cup-and-core bullets. [/QUOTE]
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Absolute Hammer actual vs Quick-load
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