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Rifles, Reloading, Optics, Equipment
Reloading
Concentricity .. how important?
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<blockquote data-quote="gte901m" data-source="post: 1456058" data-attributes="member: 80740"><p>Similar experience. Reloading is like unraveling a sweater - it never ends.</p><p></p><p>I started testing different FL dies with two batches of brass: one w/ uniformed necks (skim turned) and one virgin. Initially, concentricity was basically the same. After a few firings/loadings, concentricity flyers started appearing in both test groups. This lead me to believe something else was causing problems. All FL dies performed about the same.</p><p></p><p>Next I hypothesized case wall thickness could be causing problems. I used the RCBS concentricity tool to segregate new brass into groups of <=1 thou wall runout and >4 thou. Skim turned necks on both groups. After several firings, the >4thou wall variance group had more concentricity outliers than the <=1 thou group. Similar results across several FL dies. This led me to believe wall thickness variance was causing problems. My theory was brass flow during firing and resizing was not uniform, since wall thickness was not the same. Sure enough, after several firing, necks which began as uniform thickness (skim turned) were no longer uniform.</p><p></p><p>I ordered a set of pin gauges, and began measuring inside neck dimension of sized causes. This was a eureka moment for me. In a FL die, any thickness variance is pushed toward the ID when FL sizing. With pin gauges, you could feel this - pin would drag on one side. This was after the expander had pulled back through the neck and supposedly made it round. I then noticed (with pin gauges) after several firings, that donuts were developing at the inside neck/shoulder junction for all my brass. In my mind, its impossible for an expander to pull back through concentric when it encounters a non-symmetrical donut and a non-symmetrical neck.</p><p></p><p>Then came inside neck turning. It helped reduce FL sizing concentricity. Uniform wall thickness still produced more consistent concentricity than >4thou wall thickness. Inside neck reaming fired brass to remove donuts and skim turning necks produced the best results for all FL dies.</p><p></p><p>Then came honed and bushing dies without expanders. Similar results. Donuts don't cause concentricity issues while sizing, but due when seating a bullet. Sill have to ream donuts and turn necks for best results.</p><p></p><p>Finally the body/collet setup. I still inside neck ream to remove donuts, but don't turn necks. The collet die produced the most uniform ID of any die, which I believe maintains concentricity when seating a bullet and uniform bullet tension.</p></blockquote><p></p>
[QUOTE="gte901m, post: 1456058, member: 80740"] Similar experience. Reloading is like unraveling a sweater - it never ends. I started testing different FL dies with two batches of brass: one w/ uniformed necks (skim turned) and one virgin. Initially, concentricity was basically the same. After a few firings/loadings, concentricity flyers started appearing in both test groups. This lead me to believe something else was causing problems. All FL dies performed about the same. Next I hypothesized case wall thickness could be causing problems. I used the RCBS concentricity tool to segregate new brass into groups of <=1 thou wall runout and >4 thou. Skim turned necks on both groups. After several firings, the >4thou wall variance group had more concentricity outliers than the <=1 thou group. Similar results across several FL dies. This led me to believe wall thickness variance was causing problems. My theory was brass flow during firing and resizing was not uniform, since wall thickness was not the same. Sure enough, after several firing, necks which began as uniform thickness (skim turned) were no longer uniform. I ordered a set of pin gauges, and began measuring inside neck dimension of sized causes. This was a eureka moment for me. In a FL die, any thickness variance is pushed toward the ID when FL sizing. With pin gauges, you could feel this - pin would drag on one side. This was after the expander had pulled back through the neck and supposedly made it round. I then noticed (with pin gauges) after several firings, that donuts were developing at the inside neck/shoulder junction for all my brass. In my mind, its impossible for an expander to pull back through concentric when it encounters a non-symmetrical donut and a non-symmetrical neck. Then came inside neck turning. It helped reduce FL sizing concentricity. Uniform wall thickness still produced more consistent concentricity than >4thou wall thickness. Inside neck reaming fired brass to remove donuts and skim turning necks produced the best results for all FL dies. Then came honed and bushing dies without expanders. Similar results. Donuts don't cause concentricity issues while sizing, but due when seating a bullet. Sill have to ream donuts and turn necks for best results. Finally the body/collet setup. I still inside neck ream to remove donuts, but don't turn necks. The collet die produced the most uniform ID of any die, which I believe maintains concentricity when seating a bullet and uniform bullet tension. [/QUOTE]
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Concentricity .. how important?
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