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Rifles, Reloading, Optics, Equipment
Reloading
seating depth
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<blockquote data-quote="green 788" data-source="post: 102704" data-attributes="member: 3781"><p><strong>"But my observations have been when the bullet is seated further out, pressure and velocity go down noticably. I then increase powder to usually achieve a higher velocity at the same pressures as w/the shorter seating."</strong></p><p></p><p>This can be the case, depending on how much the base of the bullet extends into the case. The more powder room the bullet takes up, the higher the pressure spikes when the shot is fired. </p><p></p><p>As you seat the bullet farther and farther out, you relieve the pressure in the case by enlarging the space. However--when you get the bullet into the lands, the pressure begins to go up again. Since the bullet is already pressed against the lands when the powder ignites, it wants to hesitate a bit before entering the rifling (and this is one plausible explanation as to why seating close to the lands sometimes helps accuracy; it allows for a more uniform ignition of the powder). For bullets seated well away from the lands, they collide with the lands at some significant speed, and there would be little to no hesitation here.</p><p></p><p>Also, when you deep seat very long bullets, such as a VLD types, you can have--according to some ballisticians--what is called a "nail head effect." This is when there is so much of the bullet protruding into the case that it sort of "mushrooms" slightly at its base <em>before</em> leaving the case neck. Naturally, this creates a rather large pressure spike.</p><p></p><p>So basically, pressure goes high when you seat too deep, and then it reduces as you seat longer <em>until</em> you get against the lands, whereupon pressure once again increases.</p><p></p><p>I've been testing the 200 grain Sierra Matchking in my Savage LE2B .308 win. That's a long bullet, and it protrudes well into the .308 case. I found that pressure signs were MUCH worse with the bullet seated deeper into the case than they were with the bullet actually crammed into the lands about .010" or perhaps a bit more. With the bullet seated to an OAL of 2.840", I got severely stretched primer pockets and snug bolt lift with 43.8 grains of W748. But with the OAL set at 2.900", which put the bullet so far into the lands it had to be forced by the bolt to chamber, I found no pressure signs at an even higher charge of 748, which was 44.2 grains.</p><p></p><p>Dan</p></blockquote><p></p>
[QUOTE="green 788, post: 102704, member: 3781"] [b]"But my observations have been when the bullet is seated further out, pressure and velocity go down noticably. I then increase powder to usually achieve a higher velocity at the same pressures as w/the shorter seating."[/b] This can be the case, depending on how much the base of the bullet extends into the case. The more powder room the bullet takes up, the higher the pressure spikes when the shot is fired. As you seat the bullet farther and farther out, you relieve the pressure in the case by enlarging the space. However--when you get the bullet into the lands, the pressure begins to go up again. Since the bullet is already pressed against the lands when the powder ignites, it wants to hesitate a bit before entering the rifling (and this is one plausible explanation as to why seating close to the lands sometimes helps accuracy; it allows for a more uniform ignition of the powder). For bullets seated well away from the lands, they collide with the lands at some significant speed, and there would be little to no hesitation here. Also, when you deep seat very long bullets, such as a VLD types, you can have--according to some ballisticians--what is called a "nail head effect." This is when there is so much of the bullet protruding into the case that it sort of "mushrooms" slightly at its base [i]before[/i] leaving the case neck. Naturally, this creates a rather large pressure spike. So basically, pressure goes high when you seat too deep, and then it reduces as you seat longer [i]until[/i] you get against the lands, whereupon pressure once again increases. I've been testing the 200 grain Sierra Matchking in my Savage LE2B .308 win. That's a long bullet, and it protrudes well into the .308 case. I found that pressure signs were MUCH worse with the bullet seated deeper into the case than they were with the bullet actually crammed into the lands about .010" or perhaps a bit more. With the bullet seated to an OAL of 2.840", I got severely stretched primer pockets and snug bolt lift with 43.8 grains of W748. But with the OAL set at 2.900", which put the bullet so far into the lands it had to be forced by the bolt to chamber, I found no pressure signs at an even higher charge of 748, which was 44.2 grains. Dan [/QUOTE]
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