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What does this tell me?

 
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  #1  
Old 03-26-2009, 04:15 PM
tlk tlk is offline
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What does this tell me?

OK, new at this and was curious on what it would tell me:

Took a once-fired brass (shot out of my rifle), put a Sierra Matchking bullet in the brass (long), colored it with a magic marker and chambered it. Chambered fine, total length is visibily shorter and the marker is rubbed off in a little straight line almost but not completely around the bullet.

What information do I have in front of me? Anything usable or do I still need an OAL tool? Does the brass give me any reliable information regarding the proper distance for the neck and shoulder settings for my dies? Anything else? If it helps, caliber is 30-06.

Thanks for your help with this.
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Old 03-26-2009, 04:43 PM
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Re: What does this tell me?

What this tells you is that the lands of the barrel has pushed your bullet into the case that far. What it does not tell you is how far into the lands you have jammed the bullet. That will depend upon how much neck tension you had between your case neck and bullet which will determine how much force was necessary to push the bullet down into the neck and thus how far into the lands you are jammed.

What you can do now is to seat the bullet a little deeper in the case neck, like .005", recolor the bullet where the marks are and rechamber the round. If you still get the marks on the bullet then seat an additional .005", recolor and rechamber until you no longer get the marks. That way you will get a better idea exactly where the lands are.

As far as sizing on the case shoulder, the way to determine that is to close your bolt without a case in the chamber and get a "feel" for how much effort is needed to lock the lugs. Then take your fired case and chamber it and see if it takes more effort to close the bolt. If it does then you need to set your die to push the shoulder back a little.

One thing you need to be careful of is that the amount of crush fit when chambering the sized case may change from the amount of crush fit on an unsized case. IOW, when your die contacts the case body and sizes it, the sizing of the body will push the shoulder forward and create a crush fit even though you did not have a crush fit on that same case when unsized. So you can neck size (if you have a neck sizer) if you do not have a crush fit on an unsized case, you can partial neck size a case and not create a crush fit, but if you use your full length sizer to size the case body you need to check for a crush fit after sizing.

A Hornady Headspace Gauge

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

which measures on the datum line of the shoulder



and attaches to your caliper



is very useful for figuring out where to push your shoulder back to for a very slight crush fit or to push it back far enough where there is no contact but not so far that it overworks your brass.
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Old 03-26-2009, 05:36 PM
tlk tlk is offline
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Re: What does this tell me?

OK, I think I got it.

There is no difference in chambering the fired brass vs closing the bolt without it in the chamber. Made sure with a couple of other cases too. Now, with the headspace guage I can then take the measurements off of the fired brass and set up my neck sizing dies to set the shoulder the same as this case and be good to go. For full length sizing, I would use the same measurements from the guage, but need to measure the initial cases to make sure there is no crush fit. Are these steps correct?

Since the brass expands and contracts, is there any point in adjusting the dies up some from the fired case measurements to get the shoulder against the chamber as close as possible without a crush fit, or just go with the data points I have?

Thanks for the lesson.
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Old 03-26-2009, 08:05 PM
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Re: What does this tell me?

Getting there.

A couple of things.

Fired brass will grow with each successive firing until you have a crush fit. For instance this is a typical set of measurements taken with the Hornady Headspace Gauge on a factory 30-06 rifle:

New cases - 2.040" (this is with subtracting the 2" of the gauge attachement on your calipers)
Once fired - 2.0485" (neck size only)
Twice fired - 2.050" (again neck size only)
3 times fired - 2.051" (slight crush fit)
4 times fired - 2.0515" (crush fit)

Notice that the brass expands ~75% on the first firing but it is not through expanding. What is happening is that the brass has a lot of springback when new and springs back ~25% on the first firing. Upon successive firing the brass work hardens and springs back less and less until it does not have enough springback to negate the crush fit. The amount of expansion and the number of firings before a crush fit will depend upon your load, your chamber, the brass and the shape of the case. You need to understand this to get a grip on what is going on.

Another thing is that you misspoke about neck sizing

"set up my neck sizing dies to set the shoulder the same as this case and be good to go"

Neck sizing dies do not set the shoulder back. A neck sizer will only size the case neck and not any part of the body or touch the shoulder. It will be a dedicated neck sizing die and it would be called that when you bought it. If you have a standard die then in all likelihood it is a Full Length Sizing Die and it will be impossible to size all of the neck without sizing the case body and having an effect on the shoulder (whether it pushes it back or not will depend upon how you set it).

So the question would be what kind of die do you have? It will say on the box.

"Since the brass expands and contracts, is there any point in adjusting the dies up some from the fired case measurements to get the shoulder against the chamber as close as possible without a crush fit, or just go with the data points I have?"

Normally I fire a sequence like the one above and keep records in order to find out where my chamber shoulder is. You will not be able to determine your shoulder position until you start to get a crush fit. There are short cuts but it will only get more complicated if we go into those now.

There is a way to partial neck size with your Full Length Die which is a way to keep your brass expanding until it has grown to fit your chamber:

1. Raise the ram and thread the die in until it hits the shell holder
2. Lower the ram and UNTHREAD the die about 3/4 of a turn
3. Size a case and it will only size about 3/4 of the neck which is plenty to hold the bullet

This will leave a part of the neck unsized close to the shoulder



You can do this until you get a crush fit and then when you set your FL die to push the shoulder back a little it will size the entire case. Lock your die and then when you resize next time you will be close to having it set to minimally resize your case.

You only want to push the shoulder back as little as possible to get rid of the crush fit. That will extend your case life.
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Old 03-27-2009, 07:30 AM
tlk tlk is offline
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Re: What does this tell me?

Woods, what I have is a RCBS F/L sizing set and a Lee neck sizing die. I will get the headspace guage, reload my fired brass and keep the records as you suggest.
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Old 03-27-2009, 11:47 AM
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Re: What does this tell me?

So what you are saying is that even though I neck size I should probably FL size every 3rd to 4th shot depending on my gun to extend case life right?
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  #7  
Old 03-27-2009, 02:08 PM
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Re: What does this tell me?

Very interesting post. Thanks guys for the info on neck/FL sizing.
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