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338 RCM
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<blockquote data-quote="Calvin45" data-source="post: 2785079" data-attributes="member: 109862"><p>Very interesting indeed. </p><p></p><p>I've posted a thread about this phenomena in the past and called it "reverse temp sensitivity" haha. Now a difference of 8fps either way is nothing, it plainly does not matter. But the fact that you were slower at all in the heat is weird. </p><p></p><p>I have observed this, much more severely, with SUPERFORMANCE and the discontinued 8133. </p><p></p><p>Some others had observed it with a few endurons and newer temp insensitive powders. "Too much pixie dust in there" was one consensus.</p><p></p><p>Superformance I haven't know what to make of. It's not particularly sensitive to heat but isn't marketed as temp insensitive, no "pixie dust" added. But like rl17 and 26 it is a true progressive burn rate powder, not just a double base powder. These things can allow for way higher velocity under ideal circumstances but they also don't play by the same rules regarding the pressure curve and they do some weird things (also more than other powders good luck nailing down what the burn rate is - again more than other powders they can be very different animals in different cartridges)</p><p></p><p>Going from June to February with both rifle and ammo at the ambient outdoor temp, not hot rounds in a cold gun, I saw a superformance load INCREASE by 100 fps and give stiff bolt. 8133 didn't increase by as much but still increased and I'm not the only one to observe it.</p><p></p><p>Now it's been noted that this can happen in extreme cold with any powder, and a very knowledgeable member put forward that it's not that the metal of the steel contracts in any significant way (we actually tested that too) but the metal itself loses elasticity in the cold and thus can not move and flex during firing the same way. Again, this only way below freezing. -20 to -30 territory. </p><p></p><p></p><p>This likely does affect things, HOWEVER it should affect things things the same way with all powders across the board if that's all there is to this and the actual burn chemistry is not involved. It does not. No, something weird goes on with some of these newer "super powders" when the mercury drops!</p></blockquote><p></p>
[QUOTE="Calvin45, post: 2785079, member: 109862"] Very interesting indeed. I’ve posted a thread about this phenomena in the past and called it “reverse temp sensitivity” haha. Now a difference of 8fps either way is nothing, it plainly does not matter. But the fact that you were slower at all in the heat is weird. I have observed this, much more severely, with SUPERFORMANCE and the discontinued 8133. Some others had observed it with a few endurons and newer temp insensitive powders. “Too much pixie dust in there” was one consensus. Superformance I haven’t know what to make of. It’s not particularly sensitive to heat but isn’t marketed as temp insensitive, no “pixie dust” added. But like rl17 and 26 it is a true progressive burn rate powder, not just a double base powder. These things can allow for way higher velocity under ideal circumstances but they also don’t play by the same rules regarding the pressure curve and they do some weird things (also more than other powders good luck nailing down what the burn rate is - again more than other powders they can be very different animals in different cartridges) Going from June to February with both rifle and ammo at the ambient outdoor temp, not hot rounds in a cold gun, I saw a superformance load INCREASE by 100 fps and give stiff bolt. 8133 didn’t increase by as much but still increased and I’m not the only one to observe it. Now it’s been noted that this can happen in extreme cold with any powder, and a very knowledgeable member put forward that it’s not that the metal of the steel contracts in any significant way (we actually tested that too) but the metal itself loses elasticity in the cold and thus can not move and flex during firing the same way. Again, this only way below freezing. -20 to -30 territory. This likely does affect things, HOWEVER it should affect things things the same way with all powders across the board if that’s all there is to this and the actual burn chemistry is not involved. It does not. No, something weird goes on with some of these newer “super powders” when the mercury drops! [/QUOTE]
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