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Rifles, Reloading, Optics, Equipment
Reloading
Finding Jam - I thought I knew how
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<blockquote data-quote="User4302021" data-source="post: 2072587" data-attributes="member: 105322"><p>No one has ever been able to explain to me why one datum point is any more relevant than another datum point. The difference in load developement between starting from some amount of "jam" and starting from "touch" is absolutely zero.</p><p></p><p>All this hand wringing about getting the exact same measurement every single time is wasted when the seating depth "node" you are looking for is supposed to be as wide as possible anyway (something like .030" - .040" according to Berger). That is a pretty big target to hit.</p><p></p><p>If I cut a slot in the neck of a case and soft seat (jam) a bullet, then deep seat enough to back out of the lands...then my starting point is just as valid as any other starting point.</p><p></p><p>It makes absolutely no difference if I am actually .010" off "touch", or .015" off touch. The repeatability of the CBTO is only relevant <strong><em>once I start adjusting</em></strong> (either shorter or longer) from that original point.</p><p></p><p>This is the point Erik Cortina has been trying to make for a while now.</p><p></p><p>Unless you are sorting your bullets by ogive measurement, then your bullets themselves incorporate some variation. Unless all your brass is a crush fit in the chamber, the brass you size can exhibit some variation which will change the distance from the lands on any given loaded round because the ejector is exerting force on the base of the round as it sits in the chamber. Slight differences in neck tension can affect seating depth for rounds seated at the same die setting.</p><p></p><p>Wherever you start...it doesn't even need a number designation, you can call it "X". You can then work from "X" and find out if your rifle shoots at "X-.010", "X-.020"...etc.</p><p></p><p>Even if you need to chase the lands, you are STILL working from "X". If you are trying to go back and find "touch" again and work from there, then you are doing it wrong because the profile of your throat and lead has changed anyway. So .010" off of "touch" isn't the same as .010" off of "touch" when you started.</p></blockquote><p></p>
[QUOTE="User4302021, post: 2072587, member: 105322"] No one has ever been able to explain to me why one datum point is any more relevant than another datum point. The difference in load developement between starting from some amount of "jam" and starting from "touch" is absolutely zero. All this hand wringing about getting the exact same measurement every single time is wasted when the seating depth "node" you are looking for is supposed to be as wide as possible anyway (something like .030" - .040" according to Berger). That is a pretty big target to hit. If I cut a slot in the neck of a case and soft seat (jam) a bullet, then deep seat enough to back out of the lands...then my starting point is just as valid as any other starting point. It makes absolutely no difference if I am actually .010" off "touch", or .015" off touch. The repeatability of the CBTO is only relevant [B][I]once I start adjusting[/I][/B] (either shorter or longer) from that original point. This is the point Erik Cortina has been trying to make for a while now. Unless you are sorting your bullets by ogive measurement, then your bullets themselves incorporate some variation. Unless all your brass is a crush fit in the chamber, the brass you size can exhibit some variation which will change the distance from the lands on any given loaded round because the ejector is exerting force on the base of the round as it sits in the chamber. Slight differences in neck tension can affect seating depth for rounds seated at the same die setting. Wherever you start...it doesn't even need a number designation, you can call it "X". You can then work from "X" and find out if your rifle shoots at "X-.010", "X-.020"...etc. Even if you need to chase the lands, you are STILL working from "X". If you are trying to go back and find "touch" again and work from there, then you are doing it wrong because the profile of your throat and lead has changed anyway. So .010" off of "touch" isn't the same as .010" off of "touch" when you started. [/QUOTE]
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Finding Jam - I thought I knew how
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