Adjusting Die to Chamber?

Discussion in 'Reloading' started by ovastafford, Apr 3, 2010.

  1. ovastafford

    ovastafford Well-Known Member

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    I did a search on this and found some answers but none seem to answer my question. First off Im shooting 7mm rem mag and I have Redding Fl sizing die. I had the understanding that if I set my die up to where it is just touching the shell holder and size my cases, that eventually with enough firing my cases wouldnt chamber once fire formed and completely streched. I guess what I'm getting at is I have 3 time fired brass, that still fits in my chamber no problem. Whats the deal?
    Thanks
     
  2. royinidaho

    royinidaho Writers Guild

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    It's too windy to shoot so I'll give this a go...:rolleyes:

    7mm Mag is a belted case. The cartridge headspaces on the belt not the shoulder. This remains true "if" one is pushing the shoulder back, however slightly, to maintain close to the original distance from case head to shoulder.

    I suspect that resizing the cases is pretty much effortless?

    However if you back the sizing die off a few thousandths what you expect to happen will happen. The cartridge will shift to head spacing off of the shoulder as with non belted cartridges.

    IF you are satisfied with velocity and accuracy that you are now getting you are in tall cotton. No reason to change anything. Your case life will be good and your powder stocks will remain better.

    However I'll bet that if you increase the powder charge a bit you'll feel more resistance when resizing then case life will go down due to work hardening and brass flow as pressures go up.

    My saying has been 'more powder is better than less powder' and I have a bucket full of worn out cases to prove that's a dumb (and expensive) way to think.:D
     

  3. ovastafford

    ovastafford Well-Known Member

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    So I guess I dont understand what your saying, am I sizing them too much or what can I do to change this, I'm confused. Thanks for the reply, this is not an easy thing to explain.
     
  4. Scout1

    Scout1 Well-Known Member

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    I believe that what Roy is trying to say is... if your cartidge is chambering with the full length resizing and you are happy with the performance you are getting from your hand loads, don't change anything. If your not feeling the press stroke cam over at the bottom of your resizing stroke and the brass still fits in the chamber after 4 fierings, your GTG.
     
  5. ovastafford

    ovastafford Well-Known Member

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    So what your saying is Im not working my brass too much? How much life can I expect out of it. Thanks
     
  6. Moman

    Moman Well-Known Member

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    Ovastafford, if you haven't already, I would invest a minimal amount in a decent tool that will let you measure your headspace on the shoulder. With this setup, you can minimally size your shoulders back about .001-.002 and just treat them as any other bottle neck case. If you push the shoulders on these back too far you will most likely end up with case head seperation. One other area to keep an eye on is the case body just in front of the belt. Record this measurement on once fired brass, as well as brass that has been fired a few times and make sure it doesn't grow. Sometimes it will grow a little and become to large to fit in your chamber. My FL die resizes this area of the body .001 and have never had a problem with them chambering. Just the way I do it.
     
  7. ovastafford

    ovastafford Well-Known Member

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    How do I measure it?
     
  8. royinidaho

    royinidaho Writers Guild

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    Jon,

    Thanks for saying what I was trying to say.....

    I think I need to take a common sense descriptive writing class.:)
     
  9. Moman

    Moman Well-Known Member

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  10. ovastafford

    ovastafford Well-Known Member

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    Ill pick one of those up but what about the other method of chambering a fired formed case thats too tight for the chamber. Why is this not happening with my gun after three firings?
     
    Last edited: Apr 4, 2010
  11. Fitch

    Fitch Well-Known Member

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    If you are doing what I think you are doing, you set up the die like the typical manufacturer's instructions. That is, you have the shell holder pressing against the bottom of the die at the top of the ram stroke. When You size your brass, you are shoving the brass into the die till the shell holder touches which is both sizing the brass right down to the belt and bumping the shoulders back so the case is within SAAMI dimensions when you pull it out of the die. In other words, it's not happening because you are sizing the whole fireformed case back to dimensions that guarentee it will fit in the chamber.

    If, after you get your new Hornady Headspace measuring tool (which only measures headspacing for non-magnums), you back off on the sizing die and adjust it to "just" bump the shoulders back .001" or .002" you may see some hard chambering brass. The belted magnum cartridge was designed to headspace on the belt. Standard bottleneck cartridges headspace on the shoulder. By backing off on the die what you are doing is changing your brass from headspacing on the belt to headspacing on the shoulder.

    Another very useful tool is the RCBS Case Master - it allows you to measure case wall thickness just above the base where it thins as the case is used more and more. It has a long arm with a bent point on it that allows thickness measuring all the way down inside the brass. Measuring the case thinning you will see a dip in the dial indicator needle as you pass over the ring where it thinns.

    The reason for measuring this is this is where the case does most of it's stretching which causes thinning. The case fails if it gets too thin. There is a good explanation of the phenomena here with analytical animations showing the stretching phenomena:

    Rifle Chamber Finish & Friction Effects on Bolt Load and Case Head Thinning Calculations done with LS-DYNA

    He doesn't use a belted magnum case but the belted magnum acts just the same.

    Since reading his WEB page I measure all my rifle brass to see if there is thinning going on. When I see the needle "dip" more than .003" I discard the brass. The .003" dip wasn't anything scientifically derrived, I saw the dip, fired the brass once more, it didn't come apart but the dip increased to .005" and I wasn't about to shoot that brass, so I decided .003" was "my" limit for considering brass good enough to shoot. YMMV.

    It makes a lot of sense to keep brass together in batches segregated by manufacturer and number of firings. Knowing the brass history and paying attention will get the most life out of the brass with safety.

    Edited to add:

    All that said, right after writing the above I got out my brand spanking new 7mm Magnum RCBS competition die set, the set with the full length sizing die and micrometer seating die, my feeler gages, digital calipers, Hornady headspace comparitor and got ready to spend an hour adjusting the full length sizing die to bump the shoulders .001" to .002".

    Using the "E" bushing I took a fired and deprimed (but not sized) brass. Put it into the E-bushing in the calipers and set the calipers to read zero on fired brass. I did that for 5 as fired cases and they all read the same plus or minus .0005". Then I set up die per the manufacturer's instructions - that is with the case holder pressing "tightly" against the bottom of the die at the top of the stroke. Ready to begin the adjustment process, I lubed and sized the first case, wiped it off, put it back in the calipers and by golly it measured -.002". So I did another one. Same result. Third one measured -.0015", and so forth. I was ready for a session trying to get the die to bump the shouldera .001" to .002" and by happy coincidence it bumped them for an average just under .002" all on it's own adjusted per RCBS instructions. I LOVE IT when that happens!

    I tightened the set screw to freeze the lock nut, tried one more, same result and concluded this puppy was adjusted. Time to go load some ammo.

    That doesn't happen often, in fact it's the first time it's happened to me, but every now and then there is a happy relationship between the chambering reamer used by the manufacturer of the rifle and the sizing die.

    But it happened this time. I'll take it!

    Fitch
     
    Last edited: Apr 4, 2010
  12. Scout1

    Scout1 Well-Known Member

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  13. royinidaho

    royinidaho Writers Guild

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    Fitch,

    I copied your added info after the edit into MS Word, printed and stuck it to my wall.

    Great info.

    Thanks to teaching.......
     
  14. Ridge Runner

    Ridge Runner Well-Known Member

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    don't know if its right or wrong but this works for me

    I partial FL size, to set my die to my chamber, say a 7mm RM, I'll take a fired case and punch the neck out to 30 cal, then screw my die up and start resizing. when I get the neck juncture close I start trying it in the chamber, when I can feel the crush fit as the bolt goes down, I screw the die in another 1/16th turn (which is .0045" on a 14 thread) and call it good. I have some cases that have been loaded 20 times and never needed trimming.
    RR