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<blockquote data-quote="BallisticsGuy" data-source="post: 1477536" data-attributes="member: 96226"><p>All kinds of things can be causing the pressures to be different. What exactly it is? Could be, COULD BE (I'm not saying this is what's up) the jump. There are several events when you touch off a round. The primer ignites, case pressure starts to build. Then the powder ignites, case pressure builds more and very rapidly and keeps building until the neck tension is overcome and the bullet lurches forward into the rifling (causing a sudden change in effective case volume, see Boyle's Gas Law) where it encounters an impediment to its forward motion, the rifling lands. Once pressure climbs up far enough, engraving pressure is reached and the bullet proceeds through the rifling origin being fully engraved by the rifling and into the bore where its now accelerating constantly. There were a few events in that cycle that cause pressures to climb suddenly. Primer ignition, powder ignition and bullet engraving. </p><p></p><p>You're at .010" jump on the Bergers and .050 on the ABLR's. Starting with a longer jump on the Noslers, with all else being equal, the bullet will be moving faster when it hits the rifling origin and begins engraving. The increased speed at rifling contact means less gas pressure will required to move the bullet beyond that sudden point of added friction to achieve full engraving. </p><p></p><p>My bet is that if you push the Bergers into the case a little more, maybe 10-40 thousandths, that you'll see a reduction in pressure signs with that load but that's assuming that there's case capacity remaining to be taken up with the bullet shank and it won't get into charge compression. It's also assuming that bearing surface length on the bergers is actually shorter which I'd bet on. I have some 7mm ABLR and Berger Hybrids out in the garage so I guess I could measure the bearing surface length of those and make an educated guess about the actual bearing surface lengths on your .30cal pills but I'm feeling lazy and I think I sussed out the issue already anyway.</p></blockquote><p></p>
[QUOTE="BallisticsGuy, post: 1477536, member: 96226"] All kinds of things can be causing the pressures to be different. What exactly it is? Could be, COULD BE (I'm not saying this is what's up) the jump. There are several events when you touch off a round. The primer ignites, case pressure starts to build. Then the powder ignites, case pressure builds more and very rapidly and keeps building until the neck tension is overcome and the bullet lurches forward into the rifling (causing a sudden change in effective case volume, see Boyle's Gas Law) where it encounters an impediment to its forward motion, the rifling lands. Once pressure climbs up far enough, engraving pressure is reached and the bullet proceeds through the rifling origin being fully engraved by the rifling and into the bore where its now accelerating constantly. There were a few events in that cycle that cause pressures to climb suddenly. Primer ignition, powder ignition and bullet engraving. You're at .010" jump on the Bergers and .050 on the ABLR's. Starting with a longer jump on the Noslers, with all else being equal, the bullet will be moving faster when it hits the rifling origin and begins engraving. The increased speed at rifling contact means less gas pressure will required to move the bullet beyond that sudden point of added friction to achieve full engraving. My bet is that if you push the Bergers into the case a little more, maybe 10-40 thousandths, that you'll see a reduction in pressure signs with that load but that's assuming that there's case capacity remaining to be taken up with the bullet shank and it won't get into charge compression. It's also assuming that bearing surface length on the bergers is actually shorter which I'd bet on. I have some 7mm ABLR and Berger Hybrids out in the garage so I guess I could measure the bearing surface length of those and make an educated guess about the actual bearing surface lengths on your .30cal pills but I'm feeling lazy and I think I sussed out the issue already anyway. [/QUOTE]
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