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  #31  
Old 06-22-2020, 06:22 PM
Pathfinder76 Pathfinder76 is offline
 
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There is a huge variation in chamber dimensions AND die dimensions. Factory chambers are all over the map. Dies the same. I’ve got at least two sets of dies for most cartridges I load for. Some squeeze the ever living crap out of brass. So I pick the die I use accordingly. I also have custom dies built specifically for specific chambers. What a fantastic option, but the cost is insane.
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  #32  
Old 06-22-2020, 06:55 PM
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When you load up more of those upper end charges and get out for some more shooting, it would be great to hear an update with some more pics
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  #33  
Old 06-22-2020, 07:41 PM
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Will do.
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  #34  
Old 06-22-2020, 10:25 PM
Deer Hunter Deer Hunter is offline
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Quote:
Originally Posted by Dean2 View Post
DH
Give it a try, you will find Chuck is right. I was actually surprised to see the once fired having consistently higher velocity in his test till he said the 1x fired had higher neck tension.
So I took 5 identical loads from two different 308 Winchester rifles. The first bullet had low neck tension and no crimp. The second bullet I crimped lightly with a Lee Factory Crimp Die for additional neck tension. The third I crimped more. The fourth even more. The fifth was crimped very heavy almost to the point of wrecking the crimp die.

I shot them over a Labradar. There was negligible change in muzzle velocity yet the accuracy was worse.





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  #35  
Old 06-23-2020, 02:24 AM
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Ok that’s just friggin sweet you went and tested some rounds already. Makes me want to do the same.

Two questions I have from that test:
1. Does this prove Chuck’s data wrong or does it more likely imply the Lee factory crimp die may impose inconsistencies and neck tension is better created with a bushing die or the Lee collet die?
2. What is the consistency of the load without the additional factors of crimp die imposed? (Baseline of the same 5 loads first would help... instead of only one round fired without the variable of crimp imposed) I know Chuck’s data didn’t have that as he was increasing charges, but in trying to prove whether an outcome is repeatable, it would help if we minimize how many factors are introduced.
I think it would be better if several of us could test a tried and true load as is, then duplicate it with the one factor changed being neck tension. Maybe some common methods of creating the neck tension could be used too. List whether tension adjusted by:
1. Factory crimp die
2. Bushing die
3. Collet die
(Bushing die could just be rcbs fl sizer instead... either way the 1F can be tighter because work hardened slightly after firing and pulling the expander ball through doesn’t open it up as much)

Kinda thinking out loud here when I’ve got insomnia and shouldn’t be putting thoughts in writing.
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  #36  
Old 06-23-2020, 08:17 AM
DLab DLab is offline
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Also,if DH neck sized only then crimped ,his base to datum measurement wouldn't be as consistent adding slight changes to volume compared to a bushing fl. sized case.
How many times were the .308 cases fired?
Too many added variables for a fair comparison.

Chuck,
I was going to comment earlier how rounds 8-11 on your test target looked similar in results to load testing using Scott Satterlee's Ladder method that I've tried with .5 grain increases,although the brass would be the same of course,where you see a similar POI at a velocity plateau within a .5-1.5 grain load difference with a horizontal stringing effect with minimal vertical.
Also easy to find max or close to max, load limit at the same time.
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  #37  
Old 06-23-2020, 08:54 AM
Pathfinder76 Pathfinder76 is offline
 
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I agree on 8-11. I was very pleased with that.
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  #38  
Old 06-23-2020, 10:39 AM
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Completely agree way too many variables introduced.
Gonna go look up that ladder method you describe. I’ve been following the Optimal Charge Weight stuff which appears to be similar based on what you say here and looking at Chuck’s data
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  #39  
Old 06-23-2020, 02:57 PM
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Reading this thread reminded me of an article I had found on the Peterson Cartridge website a few years back that is relevant to this subject. I copied the link below. You guys might find their data to be of interest.

https://www.petersoncartridge.com/te...eated-firings/
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  #40  
Old 06-23-2020, 03:33 PM
Pathfinder76 Pathfinder76 is offline
 
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It definitely does. It’s easy to measure that, but you can also feel it when seating bullets. Re velocity. I would suspect any increase in velocity would likely be deemed statistically insignificant, and it’s increase would not be linear.
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  #41  
Old 06-24-2020, 09:50 AM
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Yeah I thought this article would be of interest as it seems to disprove the theory that increased neck tension from fired brass is responsible for increased pressure and hence velocity, which seemed to be the hypothesis from earlier in this conversation, and is something I had been curious about before as well. The Peterson findings seem to corroborate with Deer Hunters experiment (tough to tell exact numbers from their chart but velocity looks remarkable consistent) and my own findings from back when I was playing around with it. Interesting subject and good conversation.
Chuck - just curious, have you seen increased velocity related to increased neck tension from prior testing previously as well? Does anyone know of another study/data that links this relationship? I would be curious to see more data on this subject if guys are seeing different results. Thanks
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  #42  
Old 07-07-2020, 09:12 AM
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Hey guys, I've been digging into this subject a little more for my own education and found a few things. There's a pretty cool thread on an american forum some of you may be familiar with that is also super relevant to this discussion that I thought I would post here:

https://www.24hourcampfire.com/ubbth...pics/7609943/1

specifically the quote by author John Barsness: "pressure will be the same with either new or used brass of the same lot. This has been proven umpteen zillion times in pressure labs"

I've also been reading the book "Interior Ballistics: How a gun converts chemical energy into projectile motion" by E.D. Lowry and they touch on the subject with similar findings as well. It's getting a little old but that's a great book if you can get your hands on it. Anyways it's an interesting subject and gets addicting once you start going down the rabbit hole.
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  #43  
Old 07-11-2020, 10:01 AM
Pathfinder76 Pathfinder76 is offline
 
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Quote:
Originally Posted by DLab View Post
Also,if DH neck sized only then crimped ,his base to datum measurement wouldn't be as consistent adding slight changes to volume compared to a bushing fl. sized case.
How many times were the .308 cases fired?
Too many added variables for a fair comparison.

Chuck,
I was going to comment earlier how rounds 8-11 on your test target looked similar in results to load testing using Scott Satterlee's Ladder method that I've tried with .5 grain increases,although the brass would be the same of course,where you see a similar POI at a velocity plateau within a .5-1.5 grain load difference with a horizontal stringing effect with minimal vertical.
Also easy to find max or close to max, load limit at the same time.
You are on to something. :-)

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