What does this tell me?

Discussion in 'Reloading' started by tlk, Mar 26, 2009.

  1. tlk

    tlk Well-Known Member

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    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.
     
  2. woods

    woods Well-Known Member

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    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

    [​IMG]

    and attaches to your caliper

    [​IMG]

    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.
     

  3. tlk

    tlk Well-Known Member

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    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.
     
  4. woods

    woods Well-Known Member

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    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

    [​IMG]

    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.
     
  5. tlk

    tlk Well-Known Member

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    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.
     
  6. cabelas90

    cabelas90 Well-Known Member

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    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?
     
  7. 7mm Eclipse

    7mm Eclipse Well-Known Member

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    Very interesting post. Thanks guys for the info on neck/FL sizing. :)
     
  8. woods

    woods Well-Known Member

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    Not exactly. You should FL size every 3rd to 4th shot depending on your gun TO RELIEVE THE CRUSH FIT. You will get the most case life by neck sizing forever but if you develop a crush fit (and can't or don't want to live with it) then you need to FL size so that you can chamber your cases easier.

    What you don't want to do is FL size and push your shoulder back further than it needs to be pushed back. If you push it further than it needs to be then you force the case to expand more than necessary and increase work hardening which will decrease case life. It will also increase chances of a case head separation because of thinning at the pressure ring.
     
  9. foreign

    foreign Well-Known Member

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    great hread and great diagrams woods. so just to clarify for myself a crush fit is when you feel slight resistance on the bolt handle as its closed. would it be good to feel for this withouut the extractor and so on on the bolt face so there was no spring and feel from that
    cheers
     
  10. cabelas90

    cabelas90 Well-Known Member

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    Thanks that makes sense!
     
  11. woods

    woods Well-Known Member

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    I don't go that far but it is hard to feel a slight crush fit on some bolts. Some bolts have a lot of lug contact and are hard to close, even empty. However, you can definitely tell when your cases have grown enough to really bind and with the headspace gauge you can measure it and set your die to move the shoulder back .001" to .0015".

    Many reloaders do not like to have their shoulders that close because in the field and piece of trash can cause a problem and you do not want the distraction of having to grind your case into the chamber when you have game in sight and it matters. Always, give extra room for easy chambering if there is dangerous game or bears in the picture.

    One thing that is obvious is that until you reach the point where you can set the shoulder in the exact same place everytime along with sizing the case body the same everytime, you have a case that is changing. Consistancy is one of the most important elements of accuracy.