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Rifles, Reloading, Optics, Equipment
Reloading
what size groups
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<blockquote data-quote="Bart B" data-source="post: 107966" data-attributes="member: 5302"><p>[ QUOTE ]</p><p> How can a get a 2" group at 500yds and a 1" group at 100yds in theory you should have a 5" group at 500yds if the gun shoots to 1 moa at 100yds correct?</p><p></p><p>[/ QUOTE ] In theory, longer range groups will be larger than shorter range ones because bullets leaving at a slower speed drop more from gravity and drift more from non-still air movement than faster ones. And bullet drop and drift is not proportional to range. Check some ballistic tables and see what the drop and drift difference is at 100 yards for the same bullet 30 fps apart around 3000 fps, then check their drop and drift at 500 and 1000 yards; it ain't 5 and 10 times as much.</p><p></p><p>[ QUOTE ]</p><p> but how can a gun group to a tighter moa at a longer range than at a short range.</p><p></p><p>[/ QUOTE ] Easy. Shoot one group at one range, then hold and shoot better one at another range. The longer range one will usually be smaller in moa. Shoot through screens at both ranges and this won't happen unless the bullets are so poorly balanced they don't spin stabilize in their first few dozen yards of flight; but these aren't very accurate anyway. </p><p></p><p>An exception is when positive compensation causes slower bullets to leave when the muzzle axis is elevated a bit more than when faster ones are fired with the muzzle axis a bit less of an angle. Their two trajectories cross at some down range point which was common for ammo with large muzzle velocity spreads. British SMLE .303's are notorious for this with their ammo loaded with Cordite and their rear-locking bolt and receiver design. Never happened with Mauser style bolt action's front locking lugs shooting the same ammo.</p><p></p><p>[ QUOTE ]</p><p> As for the bullets having to leave the muzzle at the same velocity that to is false , I have owned guns that have had extreme spreads of as much as 30fps and would shoot under ½ moa out to 400yds.</p><p></p><p>[/ QUOTE ] With a Sierra 30 cal. 190-gr. HPMK having a 30 fps spread around 3050 fps, that will not cause vertical shot stringing more than about .04inch at 100 yards; that's .04 moa. At 400 yards, it's gonna have about a .72-inch vertical spread or .18 moa. Way down at 1000 yards vertical stringing is about 6.7 inches or .67 moa. Horizontal spread also gets non-uniformly bigger even when the air's moving in all directions only one-half mph. For each hundred yards of range the bullet goes through, the more it moves sideways from the same slight air movements because it takes longer to traverse each hundred-yard segment. Wind drift curves look much the same a bullet drop curves; they're horizontal and the drop's vertical. So groups open up in their subtended minutes of angles in all directions.</p><p></p><p>[ QUOTE ]</p><p> sometimes things happen and nobody knows why when in theory it should never be close to possible </p><p></p><p>[/ QUOTE ] When the realities of bullet flight are learned, it's all understood.</p></blockquote><p></p>
[QUOTE="Bart B, post: 107966, member: 5302"] [ QUOTE ] How can a get a 2" group at 500yds and a 1" group at 100yds in theory you should have a 5" group at 500yds if the gun shoots to 1 moa at 100yds correct? [/ QUOTE ] In theory, longer range groups will be larger than shorter range ones because bullets leaving at a slower speed drop more from gravity and drift more from non-still air movement than faster ones. And bullet drop and drift is not proportional to range. Check some ballistic tables and see what the drop and drift difference is at 100 yards for the same bullet 30 fps apart around 3000 fps, then check their drop and drift at 500 and 1000 yards; it ain’t 5 and 10 times as much. [ QUOTE ] but how can a gun group to a tighter moa at a longer range than at a short range. [/ QUOTE ] Easy. Shoot one group at one range, then hold and shoot better one at another range. The longer range one will usually be smaller in moa. Shoot through screens at both ranges and this won’t happen unless the bullets are so poorly balanced they don’t spin stabilize in their first few dozen yards of flight; but these aren't very accurate anyway. An exception is when positive compensation causes slower bullets to leave when the muzzle axis is elevated a bit more than when faster ones are fired with the muzzle axis a bit less of an angle. Their two trajectories cross at some down range point which was common for ammo with large muzzle velocity spreads. British SMLE .303's are notorious for this with their ammo loaded with Cordite and their rear-locking bolt and receiver design. Never happened with Mauser style bolt action’s front locking lugs shooting the same ammo. [ QUOTE ] As for the bullets having to leave the muzzle at the same velocity that to is false , I have owned guns that have had extreme spreads of as much as 30fps and would shoot under ½ moa out to 400yds. [/ QUOTE ] With a Sierra 30 cal. 190-gr. HPMK having a 30 fps spread around 3050 fps, that will not cause vertical shot stringing more than about .04inch at 100 yards; that’s .04 moa. At 400 yards, it’s gonna have about a .72-inch vertical spread or .18 moa. Way down at 1000 yards vertical stringing is about 6.7 inches or .67 moa. Horizontal spread also gets non-uniformly bigger even when the air's moving in all directions only one-half mph. For each hundred yards of range the bullet goes through, the more it moves sideways from the same slight air movements because it takes longer to traverse each hundred-yard segment. Wind drift curves look much the same a bullet drop curves; they're horizontal and the drop's vertical. So groups open up in their subtended minutes of angles in all directions. [ QUOTE ] sometimes things happen and nobody knows why when in theory it should never be close to possible [/ QUOTE ] When the realities of bullet flight are learned, it’s all understood. [/QUOTE]
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