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Rifles, Reloading, Optics, Equipment
Reloading
To bush or mandrel
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<blockquote data-quote="SageRatShooter" data-source="post: 2130562" data-attributes="member: 100099"><p>I've shot hundreds of groups trying to sort this question out and am still working on it. So if you want to step up your reloading game on the 375 RUM I would first consider making sure your neck thicknesses are as uniform as possible. I use an inside ball micrometer from sinclair and measure the necks in four positons. I then use a neck turner to clean up the inconsistency in the neck and usually find that 50 to 75% cleanup gets your neck thickness variation down to a few tenths of a thou. My working theory right now is that if the neck is uniform in thickness it doesn't matter if you squeeze from the outside with a bushing or push from the inside with a mandrel the resulting neck dimension inside and outside diameters will be concentric. Once you have a uniform neck geometry you can pick your neck tension so for two thou neck tension you squeeze or expand your neck so the brass ID is two thou less than the bullets diameter. When your seater pushes that bullet into the brass the brass is forced to expand that 2 thou creating the interference fit. What I found is that resistance felt in seating is still not uniform and I think that is a function of the workhardness of the brass so not all 2 thou tensions are created equal because brass hardening plays a role on the grip of the bullet at the same tension. So to really improve the neck tension and therefore SD and ES we have to start looking at annealing. Without good data to back it up my current process includes cleaning up the necks on new brass, anneal every firing, full length bushing size for 2 thou shoulder bump and neck bushing sized down 1 or 2 thou smaller than mandrel then mandrel expand back out to 1 or 2 thou neck tension.</p></blockquote><p></p>
[QUOTE="SageRatShooter, post: 2130562, member: 100099"] I've shot hundreds of groups trying to sort this question out and am still working on it. So if you want to step up your reloading game on the 375 RUM I would first consider making sure your neck thicknesses are as uniform as possible. I use an inside ball micrometer from sinclair and measure the necks in four positons. I then use a neck turner to clean up the inconsistency in the neck and usually find that 50 to 75% cleanup gets your neck thickness variation down to a few tenths of a thou. My working theory right now is that if the neck is uniform in thickness it doesn't matter if you squeeze from the outside with a bushing or push from the inside with a mandrel the resulting neck dimension inside and outside diameters will be concentric. Once you have a uniform neck geometry you can pick your neck tension so for two thou neck tension you squeeze or expand your neck so the brass ID is two thou less than the bullets diameter. When your seater pushes that bullet into the brass the brass is forced to expand that 2 thou creating the interference fit. What I found is that resistance felt in seating is still not uniform and I think that is a function of the workhardness of the brass so not all 2 thou tensions are created equal because brass hardening plays a role on the grip of the bullet at the same tension. So to really improve the neck tension and therefore SD and ES we have to start looking at annealing. Without good data to back it up my current process includes cleaning up the necks on new brass, anneal every firing, full length bushing size for 2 thou shoulder bump and neck bushing sized down 1 or 2 thou smaller than mandrel then mandrel expand back out to 1 or 2 thou neck tension. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
To bush or mandrel
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