case expansion

Discussion in 'Reloading' started by Jimm, Jul 10, 2005.

  1. Jimm

    Jimm Writers Guild

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    What should I look for when checking case expansion forwarsd of the ext. groove/belt .

    For example my new brass miked .510 before firing.

    Then on a ladder test that started with middle powder weights and progressed to listed max loads for that combo I miked the cases and got measurements onthe low end of .513 that went about half way through the test(.3 gr. increments),then gradually increase to .514 on the last (max listed ) load. There was no bolt lift change or primer flattening or cratering etc for visuals .

    This is readings after the first firing .

    Jim
     
  2. nowler

    nowler Well-Known Member

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    Mar 26, 2004
    jim

    from my understanding off it, and someone please step in if i am off the mark....

    you need to compare the size of a fired factory ammo round against your own loads. I suppose i load from half way up the load data would maybe suffice if it is a wildcat.

    anyway, given the fired factory ammo size as a datum, 4 - 5 thou over this means you are over pressure and need to back off.

    that is my understanding off it, someone tell me if i am incorrect please.

    hope it helps

    derek
     

  3. dcb

    dcb Well-Known Member

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    Jun 8, 2004
    nowler, said you need a base line to compare to and i agree.
    The method I use is for the average hand loader with a good basic knowledge of reloading.
    Take in to account that the chamber is slightly larger than the cartrage.
    The higher the pressure the more the case expands.
    I pay close attention to the expansion ring.
    I have a paper clip sharpened to a point and bent to right angle about 1/4" long. long enough to reach the inside expansion ring and lightly pull the point across the ring looking for a grouve.
    primer flatness or with an iron look can mean high pressure and the cratered indent, gas leak around the primer.shiney spots on the case head or extractor marks on the base.
    stiff bolt lift or hard extraction.
    measuring case expansion in my opinion will get you in trouble. there are other signs you need to pay attention to.
    I also use a chrono when developing loads. bullets fly best when they are loaded to a velocity suited for that bullet and rifle.
    There is a point where the velocity gain to powder ratio
    Is minimual and that is where I watch for pressure signs and some times with fast pwders that will get you in trouble.
    Hope this helps Dave
     
  4. Jimm

    Jimm Writers Guild

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    Thanks guys for your posts.

    The rifle in question is custom barreled/chambered for a std. .300 win mag. Loads mentioned were within even the reload manuals guidelines. Base line for me seems to be to check the dimensions of the new unfired brass . Then ,check the fired brass against that .This I have done ,and the ladder test with velocities recorded for each shot and case head expansion as well are matchingt the data of the manual I'm using(Sierra).

    I guess the reason I asked this quesation in the first place is that the classic pressure signs did not appear(i.e. heavy bolt lift, cratered primers,excessive shiny spots on the face of the head. Case head expansion is the only indication of max pressure that I was able to observe.
    Please , all that are so inclined , let us hear from you on this. Jim