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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
What yardage for load testing?
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<blockquote data-quote="Bart B" data-source="post: 669223" data-attributes="member: 5302"><p>Until someone proves that bullets at the outer edges of their combined trajectory paths know both where they are compared to all other bullets fired at some short range point and what direction to change to so they head back towards the point of aim at some long range, I think it's best to know that groups open up about 10% for each 100 yards down range after the first one hundered yards for front locking bolt action rifles. Positive compensation from vertical barrel whip (such as what happens with the British SMLE's) excepted. There's three things that cause that; muzzle velocity spread, a tiny spread in BC (all bullets ain't perfectly balanced) and subtle air currents.</p><p></p><p>Groups with only 3 shots are not significant enough to represent where all the shots fired will go. Good way to tell if you're shooting enough shots per test group for them to be meaningful at a given range is when all of several groups are within 10% of the same size.</p><p></p><p>All bullets are pretty well stabilized by they time they reach 100 yards. Shoot 20-shot test groups. Do it in calm conditions so the results will be meaningful. Temperature and barometric pressure don't effect accuracy as both are typically constant for a string of shots.</p><p></p><p>Note that a .308 Win. with a 50 fps muzzle velocity spread may have only 1/10th inch of vertical shot stringing at 100 yards due to velocity differences. At 1000 yards, that much velocity spread will cause a 20 inch vertical spread in bullet impact.</p></blockquote><p></p>
[QUOTE="Bart B, post: 669223, member: 5302"] Until someone proves that bullets at the outer edges of their combined trajectory paths know both where they are compared to all other bullets fired at some short range point and what direction to change to so they head back towards the point of aim at some long range, I think it's best to know that groups open up about 10% for each 100 yards down range after the first one hundered yards for front locking bolt action rifles. Positive compensation from vertical barrel whip (such as what happens with the British SMLE's) excepted. There's three things that cause that; muzzle velocity spread, a tiny spread in BC (all bullets ain't perfectly balanced) and subtle air currents. Groups with only 3 shots are not significant enough to represent where all the shots fired will go. Good way to tell if you're shooting enough shots per test group for them to be meaningful at a given range is when all of several groups are within 10% of the same size. All bullets are pretty well stabilized by they time they reach 100 yards. Shoot 20-shot test groups. Do it in calm conditions so the results will be meaningful. Temperature and barometric pressure don't effect accuracy as both are typically constant for a string of shots. Note that a .308 Win. with a 50 fps muzzle velocity spread may have only 1/10th inch of vertical shot stringing at 100 yards due to velocity differences. At 1000 yards, that much velocity spread will cause a 20 inch vertical spread in bullet impact. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
What yardage for load testing?
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