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Rifles, Reloading, Optics, Equipment
Reloading
Redding s type die advice
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<blockquote data-quote="RegionRat" data-source="post: 1604903" data-attributes="member: 57231"><p>Dusty Noggin, the difference in the headspace between the dummy case on the Stoney Point (Hornady) tool and your actual chamber, is one reason I recommended trying both methods before you assume you really know anything. The dummy round method with the ejector removed is very definitive. However, even if your shoulder has a long way to go, the same CBTO dimension applies because it doesn't use the shoulder.</p><p></p><p>All brass expands to some degree as the ignition starts, but if the CBTO is set up correctly, that bullet starts the jump at the same time regardless of how far the brass shoulder or head expand. I will theorize that you will do better with a fire-formed case that is just lightly bumped, but the CBTO value shouldn't really chase the shoulder headspace (or the belt headspace) if you have it set up correctly. The difference in pressure between a fire-formed case, and one with a huge gap, occurs when the bullet is already beyond the neck. So yes, the brass matters, but not in terms of jump.</p><p></p><p>I haven't observed huge shoulder movements on the order of 0.020" with the exception of some .303 Brit rigs, but we still set up the jump the same regardless. We see a slight drop in velocity and pressure after those .303 cases move, but it doesn't change how we look at CBTO. There will be less total difference between the runs of new loose brass versus fire-formed, if you keep the CBTO the same, as compared to adding 0.020" just to fire-form. YMMV</p></blockquote><p></p>
[QUOTE="RegionRat, post: 1604903, member: 57231"] Dusty Noggin, the difference in the headspace between the dummy case on the Stoney Point (Hornady) tool and your actual chamber, is one reason I recommended trying both methods before you assume you really know anything. The dummy round method with the ejector removed is very definitive. However, even if your shoulder has a long way to go, the same CBTO dimension applies because it doesn't use the shoulder. All brass expands to some degree as the ignition starts, but if the CBTO is set up correctly, that bullet starts the jump at the same time regardless of how far the brass shoulder or head expand. I will theorize that you will do better with a fire-formed case that is just lightly bumped, but the CBTO value shouldn't really chase the shoulder headspace (or the belt headspace) if you have it set up correctly. The difference in pressure between a fire-formed case, and one with a huge gap, occurs when the bullet is already beyond the neck. So yes, the brass matters, but not in terms of jump. I haven't observed huge shoulder movements on the order of 0.020" with the exception of some .303 Brit rigs, but we still set up the jump the same regardless. We see a slight drop in velocity and pressure after those .303 cases move, but it doesn't change how we look at CBTO. There will be less total difference between the runs of new loose brass versus fire-formed, if you keep the CBTO the same, as compared to adding 0.020" just to fire-form. YMMV [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
Redding s type die advice
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