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Rifles, Reloading, Optics, Equipment
Reloading
338 lapua pressure? HELP PLEASE
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<blockquote data-quote="Bart B" data-source="post: 514903" data-attributes="member: 5302"><p>Tests done years ago at the H.P. White Laboratory and the NRA showed peak pressure increased only about 3 to 5 percent when bullet jump to the lands went from 20 thousandths or so down to zero. Same thing was observed by folks using Oehler's strain gage pressure system. That means it goes from 50,000 CUP (or 58,000 PSI) up to a max of 52,500 CUP (60,900 PSI). That's not a dramatic pressure increase. My own crude tests measuring pressure ring diameters show about the same difference. And no brass extruded back into bolt face holes.</p><p></p><p>Most cartridge brass starts to extrude back into the bolt face cutouts at around 65,000 CUP (80,600 PSI). It only happens when pressure inside the case gets above those numbers.</p><p></p><p>I've asked several powder companies about brass starting to extrude back into bolt face ejector cutouts and they all say the same thing. The load's too high in peak pressure for safety. One's gone way past the normal and SAAMI limits for safety. The brass case is the weakest link in containing pressure and is the best indicator of pressure signs in the unsafe range.</p><p></p><p>Too much bullet extraction force to get the bullet out of the case typicaly causes much higher pressure increases than zero bullet jump to the lands. I'd measure how much force it takes to pull a seated bullet from a reloaded case. If it's more than 40 to 50 pounds, I'd be suspect of that being the reason for brass extruding into bolt face holes. I've seen this happen with sizing dies make fired case mouths too small for the bullet diameter.</p></blockquote><p></p>
[QUOTE="Bart B, post: 514903, member: 5302"] Tests done years ago at the H.P. White Laboratory and the NRA showed peak pressure increased only about 3 to 5 percent when bullet jump to the lands went from 20 thousandths or so down to zero. Same thing was observed by folks using Oehler's strain gage pressure system. That means it goes from 50,000 CUP (or 58,000 PSI) up to a max of 52,500 CUP (60,900 PSI). That's not a dramatic pressure increase. My own crude tests measuring pressure ring diameters show about the same difference. And no brass extruded back into bolt face holes. Most cartridge brass starts to extrude back into the bolt face cutouts at around 65,000 CUP (80,600 PSI). It only happens when pressure inside the case gets above those numbers. I've asked several powder companies about brass starting to extrude back into bolt face ejector cutouts and they all say the same thing. The load's too high in peak pressure for safety. One's gone way past the normal and SAAMI limits for safety. The brass case is the weakest link in containing pressure and is the best indicator of pressure signs in the unsafe range. Too much bullet extraction force to get the bullet out of the case typicaly causes much higher pressure increases than zero bullet jump to the lands. I'd measure how much force it takes to pull a seated bullet from a reloaded case. If it's more than 40 to 50 pounds, I'd be suspect of that being the reason for brass extruding into bolt face holes. I've seen this happen with sizing dies make fired case mouths too small for the bullet diameter. [/QUOTE]
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338 lapua pressure? HELP PLEASE
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