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Rifles, Reloading, Optics, Equipment
Gunsmithing
Savage M12 LRP Chamber
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<blockquote data-quote="hybridspecies" data-source="post: 2256498" data-attributes="member: 119219"><p>I'm not seeing anything on the spent brass to indicate machining defects, but I'll post some pictures soon.</p><p></p><p>The brass was virgin so I didn't set the shoulder back at all. I just used an expanding mandrel to uniform neck tension at 0.263". Using a Hornady headspace comparator, I measured the virgin brass at 1.5570" from the base to the datum and the fired brass at 1.5630" (on average). I have not yet deprimed the fired brass so these measurements might be skewed a bit.</p><p></p><p>I also used the Hornady bullet comparator and OAL gauge to measure distance to the lands for seating depth purposes. I set seating depth 0.02" deeper than what I measured. Initially I thought I might have measured incorrectly because I encountered mild resistance when inserting the OAL gauge plunger (I have another post on <a href="https://www.longrangehunting.com/threads/hornady-oal-gauge.275879/" target="_blank">this</a>), so I made a test cartridge with a magazine length seated bullet. COAL for the bullets seated 0.02" from the lands was 2.9375" and COAL for the magazine length round was 2.80". None of the bullets showed any signs of contact with the lands during cycling nor was there any resistance with the bolt. I did start to notice hard bolt lift at around 42 grains though.</p><p></p><p>Here are the measurements I took of the fired brass:</p><p></p><p>Neck Outside Diameter 0.2955"</p><p>Case Length 1.9130"</p><p>Neck Wall Thickness 0.014"</p><p>Case Diameter by Neck 0.4635"</p><p>Case Diameter by Head 0.4705"</p><p>Headspace Hornady Comp 1.5630" (with primer)</p><p></p><p>At this point I'm trying to eliminate any mechanical issues with the gun that might be causing high pressure. I spoke with Savage and the tech suggested that the firing pin spring might need to be swapped out, but I'm not sure that would result in flattened primers and ejector marks, although there is a fair amount of cratering going on. I might send the gun back with a few fired cases for them to look over as I am still within their 1 year warranty window. If it turns out that nothing's wrong, I'll probably swap out the barrel for a Shilen.</p><p></p><p>Here's a link to the borescope video I mentioned in the original post to help with diagnosis:</p><p><a href="https://youtu.be/yxUR2Vi5x4o" target="_blank">Borescope Video</a></p><p></p><p>Thanks for your thoughts, please keep them coming.</p></blockquote><p></p>
[QUOTE="hybridspecies, post: 2256498, member: 119219"] I'm not seeing anything on the spent brass to indicate machining defects, but I'll post some pictures soon. The brass was virgin so I didn't set the shoulder back at all. I just used an expanding mandrel to uniform neck tension at 0.263". Using a Hornady headspace comparator, I measured the virgin brass at 1.5570" from the base to the datum and the fired brass at 1.5630" (on average). I have not yet deprimed the fired brass so these measurements might be skewed a bit. I also used the Hornady bullet comparator and OAL gauge to measure distance to the lands for seating depth purposes. I set seating depth 0.02" deeper than what I measured. Initially I thought I might have measured incorrectly because I encountered mild resistance when inserting the OAL gauge plunger (I have another post on [URL='https://www.longrangehunting.com/threads/hornady-oal-gauge.275879/']this[/URL]), so I made a test cartridge with a magazine length seated bullet. COAL for the bullets seated 0.02" from the lands was 2.9375" and COAL for the magazine length round was 2.80". None of the bullets showed any signs of contact with the lands during cycling nor was there any resistance with the bolt. I did start to notice hard bolt lift at around 42 grains though. Here are the measurements I took of the fired brass: Neck Outside Diameter 0.2955" Case Length 1.9130" Neck Wall Thickness 0.014" Case Diameter by Neck 0.4635" Case Diameter by Head 0.4705" Headspace Hornady Comp 1.5630" (with primer) At this point I'm trying to eliminate any mechanical issues with the gun that might be causing high pressure. I spoke with Savage and the tech suggested that the firing pin spring might need to be swapped out, but I'm not sure that would result in flattened primers and ejector marks, although there is a fair amount of cratering going on. I might send the gun back with a few fired cases for them to look over as I am still within their 1 year warranty window. If it turns out that nothing's wrong, I'll probably swap out the barrel for a Shilen. Here's a link to the borescope video I mentioned in the original post to help with diagnosis: [URL='https://youtu.be/yxUR2Vi5x4o']Borescope Video[/URL] Thanks for your thoughts, please keep them coming. [/QUOTE]
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Savage M12 LRP Chamber
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