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Rifles, Reloading, Optics, Equipment
Reloading
Concentricity - setting up dies - runout
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<blockquote data-quote="boomtube" data-source="post: 504891" data-attributes="member: 9215"><p>RDM: "The way it was explained to me is that every die has some error however slight, and the same goes for every press. When you rotate the case during sizing or seating, you are spreading that error out over several points rather than all the error being in one direction."</p><p> </p><p>Yeah, it sounds reasonable, and I sure won't say it NEVER happens, but it's not normally very effective. I've tried it on too many dies of different designs to belive it. Once a bullet gets started crooked the mouth and neck have been 'bent' and it's hard to force the bullet to go in much straighter no matter how we may spin the case!</p><p> </p><p>Two things work against it. First, very few seaters are sufficently tight to forcefully correct any bullet that has started off axis. Consider that most seating stems are fairly long, they are usually of small diameter and the cup is only loosely fitted in the bullet bore and there simply isn't enough rigidity to the stem itself to push a misaligned bullet over the few thou required to straighten it out, and that also applies to the excellant Forster and Redding Comp seaters. Lee's very good seater bullet chambers are usually quite close to the indeal bullet diameter but it's short and the floating upper plug has no alignment force at all! </p><p> </p><p>Second, visualize what's happening, and where, inside the die when seating begins. The case necks are largely unsupported, or are often supported only by the case body wall against the die wall, when seating begins so seating is initiated with the case mouth and bullet heel hanging almost loosely in free space at the most critical moment. There is little at that point for even a truly rigid seating stem to work against if we do rotate it! </p><p> </p><p>Those few seaters with short sliding bullet guide sleeves, such as the current Hornady and RCBS Gold Metal, do a good job of making sure bullet heels enter the case mouth but that isn't much of a problem anyway! Older versions of the same design (from other makers) were dropped decades ago because they didn't seat any straighter than conventional seaters. Still don't; those very loosely fitted short sleeves are much less effective in loading low runout ammo than the Forster/Redding full length sleeve designs which totally align the case and bullet before seating ever begins.</p></blockquote><p></p>
[QUOTE="boomtube, post: 504891, member: 9215"] RDM: "The way it was explained to me is that every die has some error however slight, and the same goes for every press. When you rotate the case during sizing or seating, you are spreading that error out over several points rather than all the error being in one direction." Yeah, it sounds reasonable, and I sure won't say it NEVER happens, but it's not normally very effective. I've tried it on too many dies of different designs to belive it. Once a bullet gets started crooked the mouth and neck have been 'bent' and it's hard to force the bullet to go in much straighter no matter how we may spin the case! Two things work against it. First, very few seaters are sufficently tight to forcefully correct any bullet that has started off axis. Consider that most seating stems are fairly long, they are usually of small diameter and the cup is only loosely fitted in the bullet bore and there simply isn't enough rigidity to the stem itself to push a misaligned bullet over the few thou required to straighten it out, and that also applies to the excellant Forster and Redding Comp seaters. Lee's very good seater bullet chambers are usually quite close to the indeal bullet diameter but it's short and the floating upper plug has no alignment force at all! Second, visualize what's happening, and where, inside the die when seating begins. The case necks are largely unsupported, or are often supported only by the case body wall against the die wall, when seating begins so seating is initiated with the case mouth and bullet heel hanging almost loosely in free space at the most critical moment. There is little at that point for even a truly rigid seating stem to work against if we do rotate it! Those few seaters with short sliding bullet guide sleeves, such as the current Hornady and RCBS Gold Metal, do a good job of making sure bullet heels enter the case mouth but that isn't much of a problem anyway! Older versions of the same design (from other makers) were dropped decades ago because they didn't seat any straighter than conventional seaters. Still don't; those very loosely fitted short sleeves are much less effective in loading low runout ammo than the Forster/Redding full length sleeve designs which totally align the case and bullet before seating ever begins. [/QUOTE]
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Concentricity - setting up dies - runout
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