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Setting up a Full Length die.

 
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  #8  
Old 08-11-2009, 02:16 AM
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Re: Setting up a Full Length die.

Great post AJ.

I would add that in my experience as you lower the sizing die the head space can initially INCREASE as the body of the case is sized down and as the brass goes somewhere it lengthens the headspace (whilst you aren't bumping the shoulder yet). As you then screw the die in deeper it will decrease headspace again.

I found this really disconcerting when I first got a headspace gauge and measured for the first time.

I hope I'm explaining this well enough.

I suspect if your chamber is tighter this is less of an issue.
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  #9  
Old 08-11-2009, 02:48 AM
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Re: Setting up a Full Length die.

Quote:
Originally Posted by LRHWAL View Post
Great post AJ.

I would add that in my experience as you lower the sizing die the head space can initially INCREASE as the body of the case is sized down and as the brass goes somewhere it lengthens the headspace (whilst you aren't bumping the shoulder yet). As you then screw the die in deeper it will decrease headspace again.

I found this really disconcerting when I first got a headspace gauge and measured for the first time.

I hope I'm explaining this well enough.

I suspect if your chamber is tighter this is less of an issue.
LRHWAL,

You are exactly right, I was going to mention that but decided to leave out some of the details and have them discussed here. I haven't seen it happen so much with my WSM or RUM based cartridges, it may have something to do with the taper (or lack of taper) of the cartridge; I'm sure you are right and it is related to the comparative size of the die and the chamber as well.

AJ
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  #10  
Old 08-11-2009, 03:30 AM
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Re: Setting up a Full Length die.

Visualizing what LHRWAL is saying, is the brass' body not initially lengthening, and subsequently shortening as the case shoulder is engaged? If this is so, then the headspace is acting oppositely in dimension, actually decreasing initially and then increasing. I'm not refuting what is proposed, just asking if its being stated correctly.
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Old 08-11-2009, 03:35 AM
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Re: Setting up a Full Length die.

Quote:
Originally Posted by woods View Post
Great pics!

Well I ran into this in American Rifleman May 2009 issue, article on Smith & Wesson's 460XVR on page 54

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quote:
Had Hornady's engineers not had prior experience loading the .454 Casull, the 460 S&W Mag.'s case would have presented another dilemma. With pressures similar to those of the .454 Casull and production-type revolvers using the new cartridge, Mittelstaedt determined the cases needed to be "cold worked" to the brass' limits, which resulted in maximum strength/hardness, as well as better "springback". Spring back is the case's ability to, under high pressure, expand to the size of the chamber then retract enough for easy extraction. "Soft" brass doesn't "spring back", making extraction difficult.
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It always seemed to me that new brass had more springback. That was observing the behavior of the brass in my dies. I went through it on this thread

Springback - Topic Powered by Eve For Enterprise

I'm not sure if this is what you're saying here

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If you use brass that's been reloaded several times, it will not have sprung back and your measurement will be a bit longer. Your measurement will also be subject to how many times the brass has been fired.
Subsequently, I use once fired to eliminate that variable. In this example, the once fired brass measures .0045" longer than the new brass. If my once fired brass will chamber in my rifle without ANY tightness, I will attempt to resize my brass to match this number.

Once fired brass will typically spring back about .001", so matching this number will give me about .001" clearance with all my reloads.
If the Once fired brass feels tight when chambered, then I will subtract .001" from it's measurement and that will be the length I will use when adjusting the die. For this example, I'll set the resizing die to push the shoulder back to .0035" (or as close as I can make it).
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Woods,

Yep, It has always seemed to me that new brass had more spring back. Brass that has been used a lot tended to measure longer and require more resizing.

At first reading, I didn't agree with the Hornady engineers, but after some consideration, I think I do. It makes sense that as a metal gets work hardened, it tends to be more resistant to being deformed (more than when it was softer). I am certain that brass that has been shot multiple times are harder to resize. I'm also certain that once fired brass is smaller (headspace wise) than brass shot multiple times. It may be that we are trying to compare apples and oranges, and that we are using the term 'spring back' inappropriately.

If you think about shooting/resizing/shooting/resizing as a process, a cartridge will actually grow in diameter a little each cycle (because we don't have an easy method for sizing the diameter more as the brass becomes harder). We can push the shoulder back more as the brass gets harder, but we can't adjust the diameter of our dies (collet/mandrel dies excepted).

So to be correct, work hardened brass has more 'spring back', but once fired brass ends up smaller than the chamber (as compared to brass fired multiple times) because it's only been through one cycle of firing/resizing.

If you fire the same brass a half dozen times, it will pretty closely represent your chamber dimensions. New brass hasn't been processed enough times to move from it's orignal size to the chamber dimensions yet. It's tough to compare the forces involved in firing a cartridge (lots of pressure and heat) and the forces involved in resizing a piece of brass (not much pressure and almost no heat).

I read the thread you referenced and one thing intrigued me. One of the posters said that a piece of brass that is resized will grow over time (without being fired) and will behave differently whether it had been annealed or not. I went down and measured some reloads and once fired brass that has been sitting since 7/2007 and the measurements have not changed (lucky that I had documented the dimensions of the once fired and reloaded cartridges!).

OK, enough rambling.

AJ
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Last edited by AJ Peacock; 08-11-2009 at 03:40 AM.
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  #12  
Old 08-11-2009, 03:51 AM
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Re: Setting up a Full Length die.

Quote:
Originally Posted by Winchester 69 View Post
Visualizing what LHRWAL is saying, is the brass' body not initially lengthening, and subsequently shortening as the case shoulder is engaged? If this is so, then the headspace is acting oppositely in dimension, actually decreasing initially and then increasing. I'm not refuting what is proposed, just asking if its being stated correctly.

As the case body is sized, the case length will actually increase (decreasing the headspace inside a chamber). Once the shoulder is engaged, then the case length is shortened (increasing the headspace in relation to the chamber).

I think everyone is saying the same thing, just in different ways.

AJ
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  #13  
Old 08-11-2009, 06:41 AM
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Re: Setting up a Full Length die.

"Visualizing what LHRWAL is saying, is the brass' body not initially lengthening, and subsequently shortening as the case shoulder is engaged?" Yes and "As the case body is sized, the case length will actually increase (decreasing the headspace inside a chamber). Once the shoulder is engaged, then the case length is shortened (increasing the headspace in relation to the chamber)." Yes again...

I was on increasing case headspace and yes, decreasing chamber headspace. To my credit I asked if I was explaining it well
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  #14  
Old 08-11-2009, 01:49 PM
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Re: Setting up a Full Length die.

Here's a question but first let me set it up. As discussed when you set your die so that it has started resizing the case body, it starts pushing the shoulder forward. On once fired cases the shoulder is typically a few thousandths away from contacting the chamber shoulder.

Question

In your experience, when sizing once fired brass, is it possible to push the case shoulder far enough forward to contact the chamber shoulder?

Last time I checked, I was only able to push the shoulder .001" or so on once fired cases and that was not enough to enable the body die to contact the shoulder and place it exactly where I wanted it. Is there any other way to accelerate the brass expansion sequence so that you can size for a slight crush fit on once fired cases?
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