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Once fired brass and never fired brass???

 
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  #8  
Old 02-18-2010, 02:05 PM
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Re: Once fired brass and never fired brass???

Yes, that is correct. Just lube the case well and turn the F/L sizer die down about 1/8th and try again. Bolt handle should go down with some, but very little resistance. If not, repeat it again until bolt closes as above.
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  #9  
Old 02-18-2010, 09:11 PM
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Re: Once fired brass and never fired brass???

Quote:
Originally Posted by ovastafford View Post
I tried the once fired brass in my chamber unsized and the bolt was stiff to shut so I will back my die up until they fit good right?
No, backing the die up will not relieve the crush fit.

The explanation is a bit complicated but let's go through it because if you understand the entire concept then it becomes easier to make adjustments to the process.

A new case is undersized by a good amount. By that I mean that the cases are made to fit in any rifle in that particular chamber and they have to be made smaller than the smallest possible chamber out there. There are several ways to measure the amount of expansion. I use a Hornady Headspace gauge

Hornady Lock-N-Load Headspace Gage 5 Bushing Set with Comparator - MidwayUSA

that measures from the case head to a point on the shoulder close to the datum line



This is a set of typical measurements on a 30-06 I have:

New case - 2.040"
Once fired - 2.0485" (no crush fit, neck size only)
Twice fired - 2.050" (no crush fit, neck size only)
3 times fired - 2.051" (slight crush fit, neck size only)
4 times fired - 2.0515" (crush fit, neck size, body size and push the shoulder back)

Now if I push the shoulder back .001" or so for a very slight crush fit then most will call that Partial Full Length Resizing.

The Point is that in order to have 100% consistant case dimensions, you have to fire the case enough to get it fully expanded. Before that, it is in flux unless you size to set the shoulder back to once fired position everytime which in the above example would be pushing the shoulder back .003" everytime.

There is a caveat to this and it will come out in the explanation of die adjustment. The instructions for most Full Length Dies like RCBS say to adjust your die for full length as follows:

1. Raise the ram in the press and adjust the die down until the bottom of the die contacts the shell holder
2. Lower the ram and adjust the die DOWN AN ADDITION 1/8 TO 1/4

What happens when you raise a case up into the dies when it is adjusted to Full Length size is:

1. The die first contacts the case at the pressure ring just above the case head
2. When it starts sizing at the pressure ring, it squeezes the case like a balloon and it will PUSH THE SHOULDER FORWARD
3. The die continues sizing more and more of the case body until it die shoulder hits the case shoulder and begins to push it back

You can follow this process without gauges by setting your rifle up on the bench and chambering the case as you go through the sizing process. If you set your die to contact the shell holder and BACKED IT BACK UP about 1/2 to 3/4 turn, that is where the die first starts contacting the pressure ring. The case shoulder will be pushed forward, but in once fired or even twice fired it may not push the shoulder forward enough to cause a crush fit in your chamber. How much it pushes the case shoulder forward will depend upon how much the case body is being squeezed at the pressure ring which will be dependant upon the interior dimension of the die and your chamber.

If you start to get a crush fit at 1/2 turn up, then start adjusting your die down in 1/4 turns, chambering the case after each sizing. You will notice the crush fit get worse and worse. Typically the crush fit will be the worst at the point where the bottom of the die contacts the shell holder. Once you go past that point adjusting the die down (go in very small increments as each small adjustment is moving the die down a few thousanths of an inch at a time), you will get to the point where the die contacts the shoulder, starts to push it back and relieves the crush fit.

It helps to put witness marks on the die (Redding Body Die shown here)


Your rifle is the ultimate gauge. You will work your case the least and get the best case life if you keep the case shoulder in contact or very very close to contact with chamber shoulder.
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  #10  
Old 02-19-2010, 01:14 AM
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Re: Once fired brass and never fired brass???

Thanks that explains a lot. So what do I do until I get 3-4 firings in my cases? Just neck size or what? If I keep full length sizing my brass will never expand to my chamber, correct? So I need to get a neck sizing die? Thanks again!
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  #11  
Old 02-19-2010, 09:09 AM
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Re: Once fired brass and never fired brass???

I've got best accuracy with proper full length sized rimless bottle neck cases. But the fired case shoulder's not set back more than 2 thousandths. Any more and accuracy starts getting worse. One needs a case gage (RCBS Precision Mic or Hornady case gage) to measure the case from head to shoulder reference (datum) point before and after full length sizing.

In my own tests, when a rimless bottleneck fired case shoulder's set back too far, it will produce worse accuracy than when the fired case is partial neck sized such that it binds a bit with a crush fit when chamberd and the bolt's closed. Partial neck sized cases with a full length sizing die typically sets the fired case shoulder forward a bit causing a crush fit when they're chambered. There seems to be a narrow range of headspace clearance for such cases when they're full length sized. Anything outside of that degrades accuracy. This range seems to be between 2 and 3 thousandths less than chamber headspace. A fired rimless bottle neck case will have headspace about 1 thousandth less than chamber headspace; setting it back between 1 and 2 thousandths puts it in this "magical" area.

If ones rifle has a bolt face that's quite a bit out of square, new cases will typically produce the best accuracy. This was proved decades ago when the military rifle teams started using the 7.62 NATO round in their M1 and M14 rifles in competition. The armorers rebuilding these rifles with match barrels and selective fit parts never trued up the bolt faces. When a round was fired in them, the out of square bolt face made the fired case also have a way out of square head. No reloading process would fix that. Good lots of commercial 308 Win. match ammo would shoot under 4 inches all day long at 600 yards. Few people shoot handloads in bolt guns that accurate.

If one gets a crush fit with unsized fired cases in their chamber, the bolt face may be enough out of square that when the case is rotated 180 degrees from where it was when fired, the high points of the case head and bolt face are aligned. This can cause a few thousandths interference. Try chambering the fired case again but index it to a different point. If the bolt doesn't bind, then your bolt face is way out of square.

And new belted magnum cases have given me better accuracy than traditional full length sizing or any form of complete or partial neck sizing. The only way I've got fired belted magnum cases to shoot well when full length sized is when a second body sizing die is used to reduce case diameter immediately in front of the belt back to about new case diameter. Conventional full length sizing dies don't do that.

I've mentioned this before and it's worth doing it again here. Sierra Bullets full length sizes all their cases used to test their bullets. They set fired case shoulders back only a couple thousandths. I doubt anyone shoots their bullets as accurate as they do. Their web site mentions that proper full length sizing is what most competitive shooters use. And the smallest 15+ shot test groups I know of have all been fired with proper full length sized cases.

And if one can't get good accuracy full length sizing their cases, they ain't doing it the way that works best.

Last edited by Bart B; 02-19-2010 at 09:25 AM.
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  #12  
Old 02-19-2010, 09:14 AM
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Re: Once fired brass and never fired brass???

No, you do not have to get a neck sizing die. You can just set your full length die to where the bottom of the die is just touching the shell holder and resize your case. That will size the case body and all of the neck. If you do not get a crush fit then continue to size right there until you do.

However, you said you are getting a crush fit with once fired brass. Make sure it is a crush fit by closing the bolt on a empty chamber and gauging the force necessary. You may have a tight bolt fit when locking the lugs. Then close it on the case and see if there is any difference. Also there is the ejector button that adds some by pushing the case forward. It is a judgment call.

You could also blacken a case with a magic marker and see where the chamber is rubbing it off. That will tell you if your shoulder is making contact.

Anyway, like Gene said, there should be a point when threading the die 1/8 to 1/4 turn further down from where it first contacts the ram that the crush fit lessens. Find that point and set your die there to just alleviate or lessen the crush fit. That is what is important.
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  #13  
Old 02-19-2010, 11:34 AM
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Re: Once fired brass and never fired brass???

Alrighty I think I got it. Wow there is a lot to this. Thanks a lot guys, ill let you know how it goes.
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  #14  
Old 02-19-2010, 11:48 AM
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Re: Once fired brass and never fired brass???

I tested it out again and you were right. The resistance I was feeling was from the ejector. Well ill back my die up until its just touching shell holder and shoot until I get crush fit. Thanks guys!
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