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Rifles, Reloading, Optics, Equipment
Reloading
Measuring base of case to bullet ogive
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<blockquote data-quote="Kevin Thomas" data-source="post: 514406" data-attributes="member: 15748"><p>Simple. It's because you're dealing with different ogives, even if they look the same. Even changes within the same brand, caused by switching to a new form die, will show this. As a form die is used, it will occasionally need to be polished. They're solid carbide, but this repeated polishing will eventually wear a "belly" in them and they'll need to be replaced. Over the life of the die, each time it's polished, you may (MAY) see a difference, however slight in where that ogive contacts the rifling. Once that die is replaced, you're dealing with an entirely different die, that is once again on the "small" end of the specs. And that's with dies that are made to be as nearly identical as possible. When you go to a different brand of bullet, you're dealing with an entirely new set of figures. They may look alike, but those two brands will be as different as night and day. They sure won't be interchangable, not if you're looking for ultimate accuracy, anyway.</p><p> </p><p>The ogive is the radiused portion of the bullet between the meplat and the bearing surface. It's actually a French archetectual term that translates to "pointed arch" like you see in old cathederals. Each manufacturer uses something a bit different, but for the 30 cal 168 grain bullets (let's stick with that theme) they may be around 7 calibers or so. Some may use 7.1, another 7.5, etc.. Differences like this are almost impossible to see, and would need an optical comparator to discern. That, or you may just see the difference in the ogive placement when you measure them on a tool such as your Hornady. </p><p> </p><p>Let's put it this way; the difference from bolt face to rifling is a constant. When we introduce all the various shapes of different bullets, with the myriad of ogives on the market, THAT dimension (the ogive to the rifling) will change. Any clearer?</p></blockquote><p></p>
[QUOTE="Kevin Thomas, post: 514406, member: 15748"] Simple. It's because you're dealing with different ogives, even if they look the same. Even changes within the same brand, caused by switching to a new form die, will show this. As a form die is used, it will occasionally need to be polished. They're solid carbide, but this repeated polishing will eventually wear a "belly" in them and they'll need to be replaced. Over the life of the die, each time it's polished, you may (MAY) see a difference, however slight in where that ogive contacts the rifling. Once that die is replaced, you're dealing with an entirely different die, that is once again on the "small" end of the specs. And that's with dies that are made to be as nearly identical as possible. When you go to a different brand of bullet, you're dealing with an entirely new set of figures. They may look alike, but those two brands will be as different as night and day. They sure won't be interchangable, not if you're looking for ultimate accuracy, anyway. The ogive is the radiused portion of the bullet between the meplat and the bearing surface. It's actually a French archetectual term that translates to "pointed arch" like you see in old cathederals. Each manufacturer uses something a bit different, but for the 30 cal 168 grain bullets (let's stick with that theme) they may be around 7 calibers or so. Some may use 7.1, another 7.5, etc.. Differences like this are almost impossible to see, and would need an optical comparator to discern. That, or you may just see the difference in the ogive placement when you measure them on a tool such as your Hornady. Let's put it this way; the difference from bolt face to rifling is a constant. When we introduce all the various shapes of different bullets, with the myriad of ogives on the market, THAT dimension (the ogive to the rifling) will change. Any clearer? [/QUOTE]
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