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Rifles, Reloading, Optics, Equipment
Reloading
7mm RM - Higher Pressure, Lower MV Mystery
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<blockquote data-quote="Shootin4fun" data-source="post: 1301901" data-attributes="member: 28741"><p>Hi Guys,</p><p></p><p>I've been having some problems with pressure in my otherwise great shooting Savage 7mm RM so yesterday did a very controlled test comparing loads in 2 cases. Before giving the details, I'll sum up by saying in one brand of cases I'm observing higher pressure signs, but LOWER velocities than another brand of cases.</p><p></p><p>Okay, the details:</p><p></p><p>All cases prepped the same way. </p><p>Hornady vs. WW Super. </p><p>ProChrono used to measure mv.</p><p>120gr & 140gr TTSX</p><p>IMR4831, all cases individually weighed; I weigh to +/- 1 kernel as best I can with my 1980's classic RCBS 10-10</p><p>CCI250M</p><p></p><p>Hornady primers show more of a roll to their perimeters, WW Supers pretty flattened out. 1 of the 140gr rounds was much hotter for some reason (maybe due to sitting in warm chamber for 45 seconds before firing?), and the bolt was totally stuck. Had to mallet it open. Multiple groups fired over the course of the day, alternating cases and weights. Barrel heat not a factor.</p><p></p><p>Drum roll please...</p><p></p><p>Hornady rounds clocked in about 100fps higher in both 120 & 140 bullet weights! I always thought all other things being equal, higher pressure results in higher velocities. Of course if changing primers or powders we can see higher pressure with lower velocities, but that's not the case here.</p><p></p><p>Can someone explain why I'm seeing this and how it can be?</p></blockquote><p></p>
[QUOTE="Shootin4fun, post: 1301901, member: 28741"] Hi Guys, I've been having some problems with pressure in my otherwise great shooting Savage 7mm RM so yesterday did a very controlled test comparing loads in 2 cases. Before giving the details, I'll sum up by saying in one brand of cases I'm observing higher pressure signs, but LOWER velocities than another brand of cases. Okay, the details: All cases prepped the same way. Hornady vs. WW Super. ProChrono used to measure mv. 120gr & 140gr TTSX IMR4831, all cases individually weighed; I weigh to +/- 1 kernel as best I can with my 1980's classic RCBS 10-10 CCI250M Hornady primers show more of a roll to their perimeters, WW Supers pretty flattened out. 1 of the 140gr rounds was much hotter for some reason (maybe due to sitting in warm chamber for 45 seconds before firing?), and the bolt was totally stuck. Had to mallet it open. Multiple groups fired over the course of the day, alternating cases and weights. Barrel heat not a factor. Drum roll please... Hornady rounds clocked in about 100fps higher in both 120 & 140 bullet weights! I always thought all other things being equal, higher pressure results in higher velocities. Of course if changing primers or powders we can see higher pressure with lower velocities, but that's not the case here. Can someone explain why I'm seeing this and how it can be? [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
7mm RM - Higher Pressure, Lower MV Mystery
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