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Neck turning tool & Advice please

 
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  #8  
Old 12-28-2009, 09:33 AM
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Re: Neck turning tool & Advice please

There are primer pocket depth, flash hole and case head/extraction groove/rim differences that throw off weight checks -as capacity.
These do not correct themselves under pressure.
I'll concede that some lots of brass prove to more or less correlate. But there are occasional anomolies even in the best brass, so it's capacity checks or assumption.
If it matters to you, verify it.
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  #9  
Old 12-28-2009, 01:06 PM
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Re: Neck turning tool & Advice please

Quote:
Originally Posted by Mikecr View Post
There are primer pocket depth, flash hole and case head/extraction groove/rim differences that throw off weight checks -as capacity.
These do not correct themselves under pressure.
Variations in head stamp character size, quantity and depth will vary too. Neither does the variations in primer flame size and duration which cause more accuracy problems than a 1% spread in case weight or volumn.

All this aside, it's interesting to me that some folks do everything in the benchrest book to the nth degree to shoot their bullets as accurate as they can. Then others do a few simple things and shoot ammo testing groups smaller than and more often than benchrest records. There are reasons this happens.
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  #10  
Old 12-28-2009, 11:01 PM
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Re: Neck turning tool & Advice please

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Originally Posted by Bart B View Post
I disagree with the statement: "And don't qualify with brass weighing, as this may not correlate to capacity(unless it's leaves the pack in an extreme)." Case weight always correlates to "capacity" at peak pressure when the case is pressed hard against the chamber walls and bolt face.

Cartridge brass is typically the same metals in the same proportions. Some's thicker walled than others. And there's a difference in hardness. But the mass is virtually equal across all of them; about 2163 grains per cubic inch. The volumn of the brass itself is subtracted from the volumn of the chamber and what's left is the volumn of the powder burning space behind the chamber's mouth which means the working capacity of the chamber won't ever change unless the weight (volumn, mass) of the case does.

So weigh your brass then sort 'em into a 1% spread of their average weight. That's close enough to shoot as accurate as the rest of the stuff is to put the bullet where you want it.

Sorry Bart IMHO you are dead wrong on this issue. Am in Colorado with my Smith who is a HOF Shooter World Reacord Holder etc and one of the best builders on the planet and I mentioned to him that this subject is being debated again and he just shook his head. The internal capacity is all that matters and the weight of each individual piece of brass has nothing to do with internal capacity--sorry but that is a fact. Internal capacity drives pressure period.
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  #11  
Old 12-28-2009, 11:04 PM
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Re: Neck turning tool & Advice please

Quote:
Originally Posted by Bart B View Post
I disagree with the statement: "And don't qualify with brass weighing, as this may not correlate to capacity(unless it's leaves the pack in an extreme)." Case weight always correlates to "capacity" at peak pressure when the case is pressed hard against the chamber walls and bolt face.

Cartridge brass is typically the same metals in the same proportions. Some's thicker walled than others. And there's a difference in hardness. But the mass is virtually equal across all of them; about 2163 grains per cubic inch. The volumn of the brass itself is subtracted from the volumn of the chamber and what's left is the volumn of the powder burning space behind the chamber's mouth which means the working capacity of the chamber won't ever change unless the weight (volumn, mass) of the case does.

So weigh your brass then sort 'em into a 1% spread of their average weight. That's close enough to shoot as accurate as the rest of the stuff is to put the bullet where you want it.

Sorry Bart IMHO you are dead wrong on this issue. Am in Colorado with my Smith who is a HOF Shooter World Record Holder etc and one of the best builders on the planet and I mentioned to him that this subject is being debated again and he just shook his head. The internal capacity is all that matters and the weight of each individual piece of brass has nothing to do with internal capacity--sorry but that is a fact. Internal capacity drives pressure period.
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  #12  
Old 12-29-2009, 08:13 AM
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Re: Neck turning tool & Advice please

Boss exclaims:
Quote:
Sorry Bart IMHO you are dead wrong on this issue. Am in Colorado with my Smith who is a HOF Shooter World Record Holder etc and one of the best builders on the planet and I mentioned to him that this subject is being debated again and he just shook his head. The internal capacity is all that matters and the weight of each individual piece of brass has nothing to do with internal capacity--sorry but that is a fact. Internal capacity drives pressure period.
Sorry Boss IMHO I am alive right on this issue. Am in Colorado and my Smith who is a multiple time National champion, various Record Holder etc and one of the best builders on the planet and when I mentioned to him years ago that this subject is being debated he just shook his head. The internal capacity at peak pressure is all that matters and the weight of each individual piece of brass has everything to do with internal capacity--sorry but that is a fact. Internal capacity is equal to chamber volumn minus case mass volumn and that is only accurately attained at peak pressure period.

He's built rifles on Winchester Model 70 actions with standard SAAMI chambers that shoot 10-shot through 40-shot test groups from full length sized cases at 600 and 1000 yards smaller than benchrest records for the same number of shots per group.
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  #13  
Old 12-30-2009, 12:20 AM
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Re: Neck turning tool & Advice please

Bart:
Quote:
The internal capacity at peak pressure is all that matters and the weight of each individual piece of brass has everything to do with internal capacity--sorry but that is a fact.
..and

Boss:
Quote:
The internal capacity is all that matters and the weight of each individual piece of brass has nothing to do with internal capacity--sorry but that is a fact. Internal capacity drives pressure period.

Well, your both barking in the right direction..

In reality the chamber volume, case volume, and where the bullet is all change as pressure builds up during the ignition/burn sequence. Then you throw in chamber temperature and burn retardants (lube, etc) into the mix.

The chamber expands, that's what strain gauges detect when they measure chamber pressure. The case of course expands with it. Even the bolt can deform and snap back. The bullet starts to move down the barrel at a relatively low pressure. Max pressure does not occur until the bullet is a couple of inches down the barrel.

So this dynamic set of events are hard to predict. To model it, one has to go to an engineering firm that specializes in fluid flow computational analysis, and further, the modeling software they use MUST be able to handle a moving object in the stream, as well as changing volume - there are only a couple of very expensive packages that can do this kind of modeling.

Well, outside of that we experiment and try different case prep processes to try and find the factor(s) that makes the most difference. It's not exact, and that leads to comments like the above. The bottom line, think through and consider ALL factors that influence the burn sequence, consider that steel DOES deform and move about, then spring back. Then prioritize and select those factors that you think will make the most difference to your shot-to-shot consistency.


Jay
Kyle Precision Arms
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Last edited by Jay Kyle; 12-30-2009 at 12:40 AM.
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  #14  
Old 12-30-2009, 04:47 AM
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Re: Neck turning tool & Advice please

looking into getting some trimming gear too. what do you all think of the fosters case trimming tool. i have the one for doing case lengths and want to now trim neck walls to the same thicknesses so i get even releases.does the fosters system work and get it all square and good. cheers
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