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300 RUM load development questions

 
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  #78  
Old 03-15-2013, 02:31 PM
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Re: 300 RUM load development questions

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Originally Posted by Bart B View Post
Regarding a ridge on a case neck to better center it in the chamber neck......A case neck fully sized back to the shoulder will never touch a chamber neck when the round's chambered and fired. As long as the case neck's well centered on the case neck, it'll float free of contact in the chamber neck as the case shoulder's pressed hard into and well centered in the chamber shoulder.

Full length sizing case necks all the way to the shoulder bumping the shoulder back a thousandths better centers the case neck on its shoulder anyway.
I guess I don't understand you. Are you saying that in both examples the case will be centered? Is there a disadvantage or advantage to either?
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  #79  
Old 03-15-2013, 02:53 PM
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Re: 300 RUM load development questions

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Originally Posted by Bart B View Post
Cerwin, best accuracy with arms and ammo only happens when everything is as repeatable as humans can make it. This includes the bolt closing and locking up in exactly the same place for every shot. If there's any binding when the bolt's closed on a round with a "snug" fit in the chamber, the bolt won't be in the same place every time this happens. When the round fires, any strain, however slight, on the barreled action effects how it wiggles when fired.

Benchresters neck only sizing would notice this after a case had been neck sized 4 or 5 times; sometimes less. So they sized such cases with dies that set the shoulder back so there's at least a couple thousandths extra room length wise for the round to chamber without the bolt binding.

Therefore, I suggest you do something to ensure your fired case shoulders are set back at least .001" when sized. Here's a link to something very handy for making very accurate changes in sizing die height:

The Firing Line Forums

Was that ridge on the neck at the shoulder junction intended to better center the case neck in the chamber neck?
Maybe I miss spoke a bit. I do set my die to bump the shoulder back 1-2 thou. To me personally being new to loading would be snug in comparison to the headspacing I see in factory ammo. I don't have any binding closing the bolt.
As far as leaving a little donut, I'm not convinced that that would be at all beneficial to accuracy. I just leave a little to be sure I'm not in some way altering the neck shoulder junction. I'm inexperienced, and don't yet know what I can get away with and not. Just playing it safe.
I'm using an FL micrometer bushing die, so even though FL sizing, and bumping shoulders according to my measurements I still have control of how much of the neck is sized.

Thanks for that link

Last edited by cerwin; 03-15-2013 at 03:54 PM. Reason: added text
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  #80  
Old 03-15-2013, 03:04 PM
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Re: 300 RUM load development questions

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Originally Posted by cerwin View Post
I don't have any binding closing the bolt.
Likewise, no binding here. That's what I mean by snug but easy to chamber. If there is any binding I set it back until there is no binding.
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  #81  
Old 03-15-2013, 04:32 PM
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Re: 300 RUM load development questions

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Originally Posted by MontanaRifleman View Post
I guess I don't understand you. Are you saying that in both examples the case will be centered? Is there a disadvantage or advantage to either?
Yes, the case neck will be centered in both examples. Think of it being the same thing as a rimless bottleneck headspace gauge being put in a chamber. If something pushes on the back of that gauge, won't its shoulder seat fully into the chamber shoulder?

I'll continue after you've answered this question.
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  #82  
Old 03-15-2013, 06:41 PM
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Re: 300 RUM load development questions

Originally Posted by Bart B
Full length sizing case necks all the way to the shoulder bumping the shoulder back a thousandths better centers the case neck on its shoulder anyway.[/QUOTE]

So, are you suggesting that standard FL dies, rather than bushing dies may be the preffered method of correctly sizing consistently every time?

I'm pretty sure your saying that partially sizing necks is of no benefit. I realize that the shoulder is the contact point when fired and necks dont factor in to the contact point, so long as necks are centered to the case.

Last edited by cerwin; 03-15-2013 at 08:29 PM. Reason: additional text
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  #83  
Old 03-15-2013, 08:01 PM
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Re: 300 RUM load development questions

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Originally Posted by cerwin View Post

So, are you suggesting that standard FL dies, rather than bushing dies may be the preffered method of correctly sizing consistently every time?

I'm pretty sure your saying that partially sizing necks is of no benefit. I realize that the shoulder is the contact point when fired and necks dont factor in to the contact point, so long as necks are centered to the case.
While you're waiting for Bart's reply, there are two possible advantages to using a bushing. One is being able to adjust the neck tension. Some say that minimum neck tension leads to more consistent results. Another theory that is hard to prove or disprove. I have several chats with various technicians at Redding and Hornady about dies. A Redding tech said the best sizing die in his opiniong was the std FL die. The 22-250 and 25-06 cases that I recently sized with the standard New Dimension FL die have all turned out with about .001 neck runout and that was using an expander ball. Very acceptable IMO.

The other advantage, if it is an advantage, is leaving the fired donut. Again, some say this aligns the case in its fired position, neck centered in the chamber and little to movement or slop of the cartridge in chamber. Another hard one to prove or disprove. On short neck cases, the donut may be more of a disadvantage.
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  #84  
Old 03-15-2013, 08:55 PM
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Re: 300 RUM load development questions

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Originally Posted by MontanaRifleman View Post
While you're waiting for Bart's reply, there are two possible advantages to using a bushing. One is being able to adjust the neck tension. Some say that minimum neck tension leads to more consistent results. Another theory that is hard to prove or disprove. I have several chats with various technicians at Redding and Hornady about dies. A Redding tech said the best sizing die in his opiniong was the std FL die. The 22-250 and 25-06 cases that I recently sized with the standard New Dimension FL die have all turned out with about .001 neck runout and that was using an expander ball. Very acceptable IMO.

The other advantage, if it is an advantage, is leaving the fired donut. Again, some say this aligns the case in its fired position, neck centered in the chamber and little to movement or slop of the cartridge in chamber. Another hard one to prove or disprove. On short neck cases, the donut may be more of a disadvantage.
I agree on the consistent neck tension. Thats why I've been using the bushings. After sizings, repeated sizings, and firings, I read that brass is moved to the neck causing thickened necks. If so bushings would give the most consistent neck tension. Is that what your getting at here?, and does that actually become an issue? How much thickening of necks actually occurs?
I'm not convinced that a donut is of benefit, but anything is a possibility. I'm sure we'll hear more from Bart on that.
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