headspace question

Discussion in 'Reloading' started by ebsarg, Jun 15, 2012.

  1. ebsarg

    ebsarg New Member

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    I'm new to reloading for accuracy instead of cost. I bought a Hornady OAL guage and made an insert with .350" bore to measure the location of the case shoulder. My plan was to measure some fired cases and adjust the decapping/resizing die until it pushed the shoulder back .002".

    However, on both my rifles (sako 75 30-06 and sako 85 7mm rem mag) even when i screw the die all the way down all the way to the shell holder (at top of ram stroke) the location of the shoulder doesn't change.

    I measured some new winchester 7RM brass and it averaged 2.103"+/- .003 and my fired cases measure 2.120"+/- .001 so i know the cases are expanding i can repeatably measure differences in headspace.

    is it possible that the chambers in both guns are short enough that the die doesn't touch the fired cases even when it is all the way down? am i misunderstanding something? photo of my die set and measurement setup:

    [​IMG]
     
  2. Bullet bumper

    Bullet bumper Well-Known Member

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    It sounds like your chambers are a bit long if the fired brass is .017 longer than new brass . This is not such an issue with a belted case as the headspace is set by the belt untill the case is a real jam fit and then it might set on the shoulder . Even if there is .017 Approx. extra room at the shoulder the case just blows forward about .011 and back about .006 . So it is not an excessive back stretch as it would be with a non belted case .
    My advice is dump the gauge and just size the case to just rechamber paying attention to the fact that sometimes belted cases can get tight just right infront of the belt and a special collet die may be required to size that part down .
     

  3. 7stw

    7stw Well-Known Member

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    As you know, a 7 mag headspaces on the belt, not the shoulder. Here comes the caveat. That all being said, when the manufacture make the brass, they seem to make it with VERY liberal clearance between the shoulder and the chamber. I have seen as much as .030 distance on virgin brass. What this all means is that when the case is fired, it has to stretch that much to contact the shoulder. Sometimes it actually takes two firings to make full contact. Now, the effect, is the shiny ring right above the belt, which is now the weakest part of the brass. From this point on, how you size your brass, and more importantly HOW MUCH you size it, will determine how long it will last. Sometimes, and more often then not, neck sizing is your best bet, but at some point, you will have to full length size it. When that happens, the fl die needs to be set up as a bump die, to just set the shoulder back 3/1000. I have a seven mag that nearly has 9 firings on it. Brass growth has been minimal, and pockets are still tight. Neck tension is very nice, no hardening.
    All in all, it is really a combination of somewhat short brass, and liberal chambers. Proper reading, and adjusting the dies will give long life to the brass. Take care.
    P/ S, this response was originally intended for the thread opener, I clicked on the wrong reply. ( Ebsarg)
     
  4. Edd

    Edd Well-Known Member

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    If you are measuring the actual length, your fired cases are about .070" shorter than they should be. SAAMI shows 2.1162" -.007" at .420". If you move that down to .350", you will add about .075" to the length.
     
  5. LouBoyd

    LouBoyd Well-Known Member

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    ebsarge said in the first line that he's trying to load for accuracy. That's different from trying to reproduce SAAMI spec ammo. Full length resizing is generally not necessary or even desirable in most actions other than semi-autos.

    If after fired brass is run though the sizing die die it's no problem if the shoulder does not get pushed back as long as it chambers smoothly in the rifle. That is the desired situation. The brass can touch the chamber shoulder or just be close.

    It's not desirable to work (shrink and expand) dimensions of the brass more than necessary for good brass life. Custom handloads can shoot better than factory ammo mostly because it doesn't have to fit every chamber and magazine.

    Having the sizing die too long is only a problem if the brass is already to long to use. If that's the situation sets of shell holders with a range of thickness are available for that purpose. For example:
    Competition Shellholder Set #6 (7mm Remington Mag 300 Winchester Mag 338 Winchester Mag).
     
  6. Edd

    Edd Well-Known Member

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    I think you missed the point. His question was why doesn't his shoulders move when he full length sizes his fired cases. He then gives the measurement of those fired cases. Since the length of those cases are over 1/16" shorter than SAAMI and since his FL sizing die is based on SAAMI, if his measurement is correct, the shoulder isn't going to move. A .010" adjustment in shell holder height isn't going to make a difference, especially since they make the die longer. One generally uses those shell holders if you are pushing the shoulder back too far.
     
  7. LouBoyd

    LouBoyd Well-Known Member

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    I think what I missed was which direction the Redding shell holder set moves the position of the case relative to the die. I checked further and the Redding shell holders are functionally like putting a shim between the die body and the rim of the shell holder.

    ebsarge needs to make the die effectively shorter if he needs to bump longer brass back to his chamber length.

    On a rimless case like the 30-06 that could be done by just shortening the rim of a shell-lolder. On a rimmed or belted magnum case it would require shortening the face of the die and equally deepening the groove for the rim or belt.

    But unless the brass is already too long I don't see why the shoulder needs to be bumped back. The fired brass length should be ok with normal pressure loads. Its unusual to see a factory chamber on a rifle that won't accept a case sized with a standard factory die at least for for a SAAMI registered cartridge. Maybe there's some other problem, though I can't guess what. Bolts got swapped perhaps?
     
  8. ebsarg

    ebsarg New Member

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    Thank you for all the responses!

    RE: the lengths i measured relative to SAAMI specs, i bored a healthy chamfer on the leading edge of the aluminum adapter piece that beds against the case shoulder, so i'm not sure at what diameter it contacts the shoulder at, and therefor not sure where the point i am measuring is relative to the base of the cartridge. it was more a tool to see where the cases are relative to each other (so i could control the amount i was resizing). maybe i should make another at .420 to see how i compare to the spec (suspect my chambers are on the extreme short end?)

    my goal is to bump the shoulders back just enough to ensure they don't get stuck in the chamber. this hasn't happened yet, never had a sticky bolt on open or close on either gun. so maybe i don't need to worry about it? my goal is to develop sub moa hunting loads for different bullet weights, not exactly high accuracy by the standards of some.

    I fired the 7RM brass another time today (2x fired total) and it did not expand further, so i must have found the end of the chamber.

    facing the shell holder back so i can get the brass further into the die is a good idea, i'll give that a try.

    the bolts are engraved with the last 3 digits of the serial # so i'm confident the bolts in both guns are original.

    if anyone else has encountered this apparent short chamber or long die situation i'd be interested to hear about it.

    thanks for the ideas, i have a lot to learn
     
  9. Edd

    Edd Well-Known Member

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    Got any plastigage? You might use a piece of that to see if you are close to contacting the die.
     
  10. woods

    woods Well-Known Member

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    Cases can take a few firings to fully expand to the size of your chamber. So if you are attempting to push the shoulder back after only one firing then you are not setting the die down far enough and you don't want to. You need to let the case expand enough to hit the shoulder before you start pushing the shoulder back with the die.

    For example here are some measurements taken with a Hornady "Headspace" Gauge (even though not headspace on a belted case) with the proper insert that measures close to the datum line on a 300 win mag:

    new case - 2.253"
    once fired - 2.270" - neck sized with Lee Collet
    twice fired - 2.272" - slight crush fit, neck sized with Lee Collet
    3 times fired - 2.2725" - crush fit, push shoulder back

    The point is that on the first firing the shoulder was still .0025" from expanding fully to fit the chamber. If you took a measurement on this firing and pushed the shoulder back .001" or .002" and decided that is your measurement and did it everytime, you would be forcing the brass to expand .0035" or .0045" every firing. This would accelerate thinning at the web, shorten brass life and possibly lead to a case head separation.

    The best way is to chamber your fired brass in your gun and let it tell you when it is time to push the shoulder back.